Question 29: (i) show that the points A(5,6), 8(1, 5), C(2,1) and D(6,2) are the vertices of a square.

(ii) Prove that the points A (2,3), B(-2,2),C(-1,-2) , and D(3,-1) are the vertices of a square ABCD .

(iii) Name the type of \triangle PQR   formed by the points P(\sqrt{2}, \sqrt{2}), Q( -\sqrt{2}, -\sqrt{2}) , and R(-\sqrt{6}, \sqrt{6})  

Answer:

i) Let the points be A(5,6), B(1, 5), C(2, 1) and D(6, 2)

Therefore sides of the figure

AB = \sqrt{(5-1)^2 + (6-5)^2 }= \sqrt{16+1} = \sqrt{17}

BC = \sqrt{(1-2)^2 + (5-1)^2 }= \sqrt{1+16} = \sqrt{17}

CD = \sqrt{(2-6)^2 + (1-2)^2 }= \sqrt{16+1} = \sqrt{17}

DA = \sqrt{(6-5)^2 + (2-6)^2 }= \sqrt{1+16} = \sqrt{17}

Diagonals of the figure

AC= \sqrt{(5-2)^2 + (6-1)^2 }= \sqrt{9+25} = \sqrt{34}

BD = \sqrt{(1-6)^2 + (5-2)^2 }= \sqrt{25+9} = \sqrt{34}

Hence, AB = BC=CD=DA . Also diagonals are equal. Therefore the figure is a square.

ii) Let the points be A(2,3), B(-2,2), C(-1,-2) and D(3, -1)

Therefore sides of the figure

AB = \sqrt{(2+2)^2 + (3-2)^2 }= \sqrt{16+1} = \sqrt{17}

BC = \sqrt{(-2+1)^2 + (2+2)^2 }= \sqrt{1+16} = \sqrt{17}

CD = \sqrt{(-1-3)^2 + (-2+1)^2 }= \sqrt{16+1} = \sqrt{17}

DA = \sqrt{(3-2)^2 + (-1-3)^2 }= \sqrt{1+16} = \sqrt{17}

Diagonals of the figure

AC= \sqrt{(2+1)^2 + (3+2)^2 }= \sqrt{9+25} = \sqrt{34}

BD = \sqrt{(-2-3)^2 + (2+1)^2 }= \sqrt{25+9} = \sqrt{34}

Hence, AB = BC=CD=DA . Also diagonals are equal. Therefore the figure is a square.

iii) Let the points be P(\sqrt{2}, \sqrt{2}), Q( -\sqrt{2}, -\sqrt{2}), R(-\sqrt{6}, \sqrt{6})

Therefore sides of the figure

PQ = \sqrt{(\sqrt{2} + \sqrt{2})^2 + (\sqrt{2} + \sqrt{2})^2 }= \sqrt{8+8} = \sqrt{16}

QR = \sqrt{(-\sqrt{2} + \sqrt{6})^2 + (-\sqrt{2} - \sqrt{6})^2 }= \sqrt{2+ 6 - 2 \sqrt{12}+ 2 + 6 + 2\sqrt{12}} = \sqrt{16}

RP = \sqrt{(-\sqrt{6} - \sqrt{2})^2 + (\sqrt{6} - \sqrt{2})^2 }= \sqrt{6+ 2 + 2 \sqrt{12}+ 6 + 2 - 2\sqrt{12}} = \sqrt{16}

Hence, PQ = QR = RP . Therefore the figure is an equilateral triangle.

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Question 30: Find the point on x-axis which is equidistant from the points (-2, 5) and (2,-3) .

Answer:

Given A ( -2, 5), B ( 2, -3)

Let the equidistant point be O(x, 0)

OA = OB \Rightarrow OA^2 = OB^2

\Rightarrow (x+2)^2 + ( 0-5)^2 = (x-2)^2 + (0+3)^2

\Rightarrow x^2 + 4 + 4x + 25 = x^2 + 4 - 4x + 9

\Rightarrow 8x = -29 + 13

\Rightarrow 8x = -16

\Rightarrow x = -2

Therefore point is ( -2, 0)

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Question 31: Find the value of x such that PQ = QR where the coordinates of P, Q and R are (6,-1), (1,3) and (x,8) respectively.

Answer:

Given: P(6, -1), Q(1, 3), R(x, -8)

PQ = QR \Rightarrow PQ^2 = QR^2

\Rightarrow (1-6)^2 + ( 3+1)^2 = ( x-1)^2 + ( 8-3)^2

\Rightarrow 25 + 16 = x^2 + 1 - 2x + 25

\Rightarrow x^2 - 2x - 15 = 0

\Rightarrow (x-5)(x+3) = 0

\Rightarrow x = 5 \ or \  -3

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Question 32: Prove, that the points (0, 0), (5,5) and (-5, 5) are the vertices of a right isosceles triangle.

Answer:

Let the points be A(0,0), B(5,5), C(-5, 5)

Therefore sides of the figure

AB = \sqrt{(5-0)^2 + (5-0)^2 }= \sqrt{25+25} = \sqrt{50}

BC = \sqrt{(-5-5)^2 + (5-5)^2 }= \sqrt{100} 

CA = \sqrt{(-5-0)^2 + (5-0)^2 }= \sqrt{25+25} = \sqrt{50}

Since AB = CA, \triangle ABC is an Isosceles triangle.

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Question 33: If the point P(x, y) is equidistant from the points A(5,1) and B(1,5) , prove that x=y .

Answer:

Given: A(5, 1), B(1, 5) , P(x, y)

AP = BP \Rightarrow AP^2 = BP^2

\Rightarrow ( x-5)^2 + ( y - 1)^2 = (x-1)^2 + ( y - 5)^2

\Rightarrow x^2 + 25 - 10x + y^2 + 1 - 2y = x^2 + 1 - 2x + y^2 + 25 - 10y

\Rightarrow 26 - 10x - 2y = 26 - 2x - 10y

\Rightarrow -8x = - 8y

\Rightarrow x = y

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Question 34: If Q (0, 1 ) is equidistant from P (5, -3) and R (x, 6) , find the values of x . Also, find the distances QR and PR .

Answer:

Given: P(5, -3), R(x, 6) , Q (0, 1)

QP = QR \Rightarrow QP^2 = QR^2

\Rightarrow (0-5)^2 + ( 1+3)^2 = (0-x)^2 + ( 1-6)^2

\Rightarrow 25 + 16 = x^2 + 25

\Rightarrow x = \pm 4

When x = 4, QR = \sqrt{4^2 + 25} = \sqrt{16 + 25} = \sqrt{41} units

When x = -4, QR = \sqrt{(-4)^2 + 25} = \sqrt{16 + 25} = \sqrt{41} units

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Question 35: Find the values of y for which the distance between the points P (2, -3) and Q (10, y) is 10 units.

Answer:

Given: P(2, -3), Q(10, y) , PQ =10

(10-2)^2 + (y+3)^2 = 10^2

\Rightarrow 64 + ( y + 3)^2 = 100

\Rightarrow ( y + 3) ^2 = 36

\Rightarrow y + 3 = \pm 6

\Rightarrow y = 3, -9

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Question 36: Find the center of the circle passing through (6, -6), (3,-7) and (3, 3) .

Answer:

Given: A ( 6, -6), B(3, -7), C ( 3,3)

Let center be O(x, y)

OA^2 = ( x-6)^2 + ( y+6)^2

OB^2 = ( x-3)^2 + ( y+7)^2

OC^2 = ( x-3)^2 + ( y-3)^2

OA^2 = OB^2

\Rightarrow ( x-6)^2 + ( y+6)^2 = ( x-3)^2 + ( y+7)^2

\Rightarrow x^2 + 36 - 12 x + y^2 + 36 + 12 y = x^2 + 9 - 6x + y^2 + 49 + 14 y

\Rightarrow 72-12x+12y = 58 - 6x +14y

\Rightarrow 14 = 6x + 2y

\Rightarrow 3x+y = 7    … … … … … i)

OB^2 = OC^2

\Rightarrow ( x-3)^2 + ( y+7)^2 = ( x-3)^2 + ( y-3)^2

\Rightarrow y^2 + 49 + 14y = y^2 +9 - 16y

\Rightarrow 20y = - 40

\Rightarrow y = -2    … … … … … ii)

Substituting in i)

3x + ( -2) = 7

\Rightarrow 3x = 9

\Rightarrow x = 3

Therefore center is ( 3, -2)

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Question 37: Two opposite vertices of a square are (-1,2) and (3,2) . Find the coordinates of other two vertices.

Answer:

Given A ( -1, 2), C(3, 2) , B(x, y)

AB^2 = BC^2

\Rightarrow (x+1)^2 + ( y - 2)^2 = ( x-3)^2 + ( y - 2)^2

\Rightarrow x^2 + 1 + 2x + y^2 + 4 - 4x = x^2 + 9 -6x + y^2 + 4 - 4y

\Rightarrow 1+2x = 9-6x

\Rightarrow 8x = 8

\Rightarrow x= 1    … … … … … i)

Also

AB^2 + BC^2 = AC^2

\Rightarrow (x+1)^2 + ( y - 2)^2 + ( x-3)^2 + ( y - 2)^2 = ( 3+1)^2 + ( 2- 2)^2

\Rightarrow x^2 + 1 + 2x + y^2 + 4 - 4y + x^2 + 9 - 6x + y^2 + 4 - 4y = 16

\Rightarrow 2x^2 + 2y^2 - 4x - 8y + 2 = 0

From i), x = 1

\Rightarrow 2 + 2y^2 - 4 - 8y + 2 = 0

\Rightarrow 2y^2 - 8y= 0

\Rightarrow y^2 - 4y=0

\Rightarrow y( y - 4) = 0

\Rightarrow y = 0 \ or \ y = 4

Hence the coordinates are B( 1, 4), D(1, 0)

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Question 38: Name the quadrilateral formed, if any, by the following points, and give reasons for your answers:

(i) A (-1, - 2), B(1, 0), C (-1, 2),D (-3, 0)

(ii) A (-3, 5), B (3, 1),C (0, 3), D (-1, -4)

(iii) A (4,5), B (7 ,6), C (4,3), D (1,2)

Answer:

i)    Let the points be A(-1, -2), B(1,0), C(-1,2) and D(-3,0)

Therefore sides of the figure

AB = \sqrt{(1+1)^2 + (0+2)^2 }= \sqrt{4+4} = \sqrt{8}

BC = \sqrt{(-1-1)^2 + (2-0)^2 }= \sqrt{4+4} = \sqrt{8}

CD = \sqrt{(-3+1)^2 + (0-2)^2 }= \sqrt{4+4} = \sqrt{8}

DA = \sqrt{(-3+1)^2 + (0+2)^2 }= \sqrt{4+4} = \sqrt{8}

Diagonals of the figure

AC= \sqrt{(-1+1)^2 + (2+2)^2 }= \sqrt{16} = 4

BD = \sqrt{(-3-1)^2 + (0-0)^2 }= \sqrt{16} = 4

All four sides are equal and also the diagonals are equal. Hence this is a square.

ii)   Let the points be A(-3, 5), B(3, 1), C(0, 3) and D(-1,-4)

Therefore sides of the figure

AB = \sqrt{(3+3)^2 + (1-5)^2 }= \sqrt{81+16} = \sqrt{97}

BC = \sqrt{(0-3)^2 + (3-1)^2 }= \sqrt{9+4} = \sqrt{13}

CD = \sqrt{(-1-0)^2 + (-4-3)^2 }= \sqrt{1+49} = \sqrt{50}

DA = \sqrt{(-1+3)^2 + (-4-5)^2 }= \sqrt{4+81} = \sqrt{85}

All four sides are unequal . Hence this is a quadrilateral.

iii)  Let the points be A(4,5), B(7,6), C(4,3) and D(1,2)

Therefore sides of the figure

AB = \sqrt{(7-4)^2 + (6-5)^2 }= \sqrt{9+1} = \sqrt{10}

BC = \sqrt{(4-7)^2 + (3-6)^2 }= \sqrt{9+9} = \sqrt{18}

CD = \sqrt{(1-4)^2 + (2-3)^2 }= \sqrt{9+1} = \sqrt{10}

DA = \sqrt{(1-4)^2 + (2-5)^2 }= \sqrt{9+9} = \sqrt{18}

Diagonals of the figure

AC= \sqrt{(4-4)^2 + (3-5)^2 }= \sqrt{4} = 2

BD = \sqrt{(1-7)^2 + (2-6)^2 }= \sqrt{36+16} = \sqrt{52}

All four sides are equal and but the diagonals are unequal, this is a Rhombus.

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Question 39: Find the equation of the perpendicular bisector of the line segment joining points (7,1) and (3,5) .

Answer:

Given: A ( 7, 1), B ( 3, 5)

Mid point of AB = \Big( \frac{7+3}{2} , \frac{1+5}{2} \Big) = (5, 3)

Slope of AB = \frac{5-1}{3-7} = \frac{4}{-4} = -1

Therefore slope of perpendicular bisector = 1

Therefore equation of perpendicular bisector  is

y - 3 = 1 ( x - 5)

\Rightarrow y = x - 2

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Question 40: Prove that the points (3, 0), (4, 5), (-1, 4) and (-2, -1) , taken in order, form a rhombus. Also, find its area.

Answer:

Let the points be A(3,0), B(4,5), C(-1,4) and D(-2,-1)

Therefore sides of the figure

AB = \sqrt{(4-3)^2 + (5-0)^2 }= \sqrt{1+25} = \sqrt{26}

BC = \sqrt{(-1-4)^2 + (4-5)^2 }= \sqrt{25+1} = \sqrt{26}

CD = \sqrt{(-2+1)^2 + (-1-4)^2 }= \sqrt{1+25} = \sqrt{26}

DA = \sqrt{(-2-3)^2 + (-1-0)^2 }= \sqrt{25+1} = \sqrt{26}

Diagonals of the figure

AC= \sqrt{(-1-3)^2 + (4-0)^2 }= \sqrt{16+16} = 4\sqrt{2}

BD = \sqrt{(-2-4)^2 + (-1-5)^2 }= \sqrt{36+36} = \sqrt{72} = 6\sqrt{2}

All four sides are equal and but the diagonals are unequal, this is a Rhombus.

Area of the Rhombus = \frac{1}{2} (product of diagonals)

= \frac{1}{2} \times 4\sqrt{2} \times 6\sqrt{2} = 24 sq. units.

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Question 41: ln the seating arrangement of desks in a classroom three students Rohini, Sandhya and Bina are seated at A (3, 1), B (6,4) and C (8, 6) . Do you think they are seated in a line?

Answer:

Given: A ( 3, 1), B ( 6, 4) , C(8, 6)

AB = \sqrt{(6-3)^2 + (4-1)^2 }= \sqrt{9+9} = 3\sqrt{2}

BC = \sqrt{(8-6)^2 + (6-4)^2 }= \sqrt{4+4} = 2\sqrt{2}

CA = \sqrt{(3-8)^2 + (1-6)^2 }= \sqrt{25+25} = 5\sqrt{2}

\Rightarrow AB + BC = CA

Hence they are all in a straight line.

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Question 42: Find a point on y-axis which is equidistant from the points (5 , - 2) and (- 3, 2) .

Answer:

Given: A ( 5, -2), B ( -3, 2)

Let the equidistant point be O(0, y)

Given OA = OB \Rightarrow OA^2 = OB^2

Therefore (0-5)^2 + ( y + 2)^2 = ( 0+3)^2 + ( y - 2)^2

\Rightarrow 25 + y^2 + 4 + 4y = 9 + y^2 + 4 - 4y

\Rightarrow 29 + 4y = 13 - 4y

\Rightarrow 8y = - 16

\Rightarrow y = -2

Therefore the point is (0, -2)

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Question 43: Find a relation between x and y such that the point (x, y) is equidistant from the points (3,6) and (-3,4) .

Answer:

Given A ( 3, 6), B ( -3, 4)

Let equidistant point O(x, y)

Given OA = OB \Rightarrow OA^2 = OB^2

\Rightarrow (x-3)^2 + ( y - 6)^2 = (x+3)^2 + ( y -4)^2

\Rightarrow x^2 + 9 - 6x + y^2 + 36 - 12y = x^2 + 9 + 6x + y^2 + 16 - 4y

\Rightarrow 45 - 6x - 12y = 25 + 6x - 8y

\Rightarrow 12x + 4y = 20

\Rightarrow 3x + y = 5

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Question 44: If a point A(0,2) is equidistant from the points B (3,p) and C(p,5) , then find the value of p .

Answer:

Given: A(0, 2), B(3, p), C(p, 5)

Since AB = AC \Rightarrow AB^2 = AC^2

\Rightarrow (3-0)^2 + ( p-2)^2 = ( p - 0)^2 + ( 5-2)^2

\Rightarrow 9+p^2 +4 - 4p = p^2 + 9

\Rightarrow 13-4p = 9

\Rightarrow 4p = 4

\Rightarrow p = 1

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Question 45: Prove that the points (7, 10), (-2,5) and (3, -4) are the vertices of an isosceles right triangle.

Answer:

Given: A ( 7, 10), B ( -2, 5) , C(3, -4)

AB = \sqrt{(-2-7)^2 + (5-10)^2 }= \sqrt{81+25} = \sqrt{106}

BC = \sqrt{(3+2)^2 + (-4-5)^2 }= \sqrt{25+81} = \sqrt{106}

CA = \sqrt{(7-3)^2 + (10+4)^2 }= \sqrt{16+196} = \sqrt{212}

Therefore AB = AC ( i.e. two sides of the triangle are equal)

Also AB^2 + BC^2 = AC^2

\Rightarrow 106 + 106 = 212

Therefore \triangle ABC is a right angled isosceles triangle.

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Question 46: If the point P(x, 3) is equidistant from the points A(7,-1) and B(6,8) , find the value of x and find the distance AP .

Answer:

Give: P(x, 3), A ( 7, -1), B(6, 8)

Since PA = PB \Rightarrow PA^2 = PB^2

\Rightarrow (7-x)^2 + ( -1 -3)^2 = (6-x)^2 + (8-3)^2

\Rightarrow 49 + x^2 - 14x + 16 = 36 + x^2 - 12x + 25

65 - 14x = 61 - 12x

4 = 2x \ or \ x = 2

Hence the point is (2, 3)

AP = \sqrt{(7-2)^2 + ( -1-3)^2} = \sqrt{25+16} = \sqrt{41}

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Question 47: It A(3,y) is equidistant from points P (8,-3) and Q(7,6) , find the value of y and find the distance AP .

Answer:

Given: A ( 3, y), P(8, -3) , Q(7,6)

Since AP = AQ \Rightarrow AP^2 = AQ^2

\Rightarrow (8-3)^2 + ( -3-y)^2 = ( 7-3)^2 + ( 6-y)^2

\Rightarrow 25 + 9 + y^2 + 6y = 16 + 36 + y^2 - 12y

\Rightarrow 34 + 6y = 52 - 12y

\Rightarrow 18 y = 18

\Rightarrow y = 1

Therefore A ( 3, 1)

AP = \sqrt{(8-3)^2 + ( -3-1)^2} = \sqrt{25+16} = \sqrt{41}

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Question 48: If (0, - 3) and (0, 3) are the two vertices of an equilateral triangle, find the coordinates of its third vertex.

Answer:

Given: A (0, -3), B(0, 3)

Let third vertices be C(x, y)

AC^2 = ( x-0)^2 + (y+3)^2

AB^2 = ( 0-0)^2 + ( 3+3)^2 = 36

BC^2 = (x-0)^2 + (y-3)^2

Since AC^2 = AB^2

\Rightarrow x^2 + (y+3)^2 = 36

\Rightarrow x^2 + y^2 + 9 + 6y = 36

or \Rightarrow x^2 + y^2 + 6y = 27  … … … … … i)

AC^2 = BC^2

\Rightarrow x^2 + (y+3)^2 = x^2 + ( y-3)^2

\Rightarrow x^2 + y^2 +9 + 6y = x^2 + y^2 + 9 - 6y

\Rightarrow 9 + 6y = 9 - 6y

\Rightarrow 12y = 0

\Rightarrow y = 0

Substituting in i)

x^2 = 27 \Rightarrow x = \pm 3\sqrt{3}

Therefore C could be ( 3\sqrt{3}, 0) or (- 3\sqrt{3}, 0)

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Question 49: If the point P (2, 2) is equidistant from the point s A (-2, k) and B (-2k, 3) , find k . Also, find the length of AP .

Answer:

Given: P(2, 2), A ( -2, k), B ( -2k, -3)

AP^2 = ( -2-2)^2 + ( k-2)^2 = 16 + ( k-2)^2

BP^2 = (-2k-2)^2 + ( -3-2)^2 = ( -2k-2)^2 + 25

AP^2 = BP^2

\Rightarrow 16 + ( k-2)^2 = ( -2k-2)^2 + 25

\Rightarrow k^2 + 4 - 4k = 9 + 4k^2 + 4 + 8k

\Rightarrow 3k^2 + 12k + 9 = 0

\Rightarrow k^2 + 4k + 3 = 0

\Rightarrow (k+3)(k+1)=0

\Rightarrow k = -3 \ or \ k = -1

If k = -3 \Rightarrow AP = \sqrt{(-2-2)^2+(-3-2)^2} = \sqrt{16+25} = \sqrt{41}

If k = -1 \Rightarrow AP = \sqrt{(-2-2)^2+(-1-2)^2} = \sqrt{16+9} = \sqrt{25} = 5

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Question 50: If the point A(0,2) is equidistant from the points B(3,p) and C(p,5) , find p . Also, find the length of AB .

Answer:

Given: A(0, 2), B(3, p), C(p, 5)

AB^2 = ( 3-0)^2 + ( p-2)^2

AC^2 = (p-0)^2 + ( 5-2)^2

AB^2 = AC^2

(3-0)^2 + ( p - 2)^2 = ( p-0)^2 + (5-2)^2

9+p^2+4 - 4p = p^2 + 9

4-4p = 0

p=1

Therefore AB = \sqrt{9 + ( 1-2)^2 } = \sqrt{10}

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Question 51: If the point P (k -1,2) is equidistant from the points A(3,k) and B(k, 5) , find the values of k .

Answer:

Given: P(k-1, 2), A(3, k), B(k, 5)

AP^2 = ( 3-k+1)^2 + ( k-2)^2 = (4-k)^2 + ( k-2)^2

BP^2 = (k-k+1)^2 + ( 5-2)^2 = 1+9 = 10

AP^2 = BP^2

\Rightarrow (4-k)^2 + ( k-2)^2 =10

\Rightarrow 16 +k^2 -8k + k^2 + 4 - 4k = 10

\Rightarrow 2k^2 - 12k + 20 = 0

\Rightarrow k^2 -6k + 5 = 0

\Rightarrow (k-1)(k-5) = 0

\Rightarrow k = 1 \ or \ k = 5

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Question 52: If (-4,3) and (4,3) are two vertices of an equilateral triangle, find the coordinates of the third vertex, given that the origin lies in the (i) interior, (ii) exterior of the triangle.

Answer:

Given: A (-4, 3), B(4, 3)

Let third vertices be C(x, y)

AB^2 = (4+4)^2 + ( 3- 3)^2 = 64

BC^2 = ( x-4)^2 + ( y - 3)^2

AC^2 = ( x+ 4)^2 + ( y - 3)^2

BC^2 = AC^2

\Rightarrow ( x-4)^2 + ( y - 3)^2 = ( x+ 4)^2 + ( y - 3)^2

\Rightarrow x^2 + 16 - 8x = x^2 + 16 + 8x

\Rightarrow 16x = 0

\Rightarrow x = 0

BC^2 = AB^2

\Rightarrow ( x-4)^2 + ( y - 3)^2 = 64

\Rightarrow 16 + (y-3)^2 = 64

\Rightarrow (y-3)^2 = 48

\Rightarrow y - 3 = \pm 4\sqrt{3}

\Rightarrow y = 3 \pm 4\sqrt{3}

Hence C is i) (0, 3 - 4\sqrt{3}) and ii) ( 0, 3+4\sqrt{3})

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Question 53: Ayush starts walking from his house to office. Instead of going to the office directly, he goes to a bank first, from there to his daughter’s school and then reaches the office. What is the extra distance traveled by Ayush in reaching the office? (Assume that all distances covered are in straight hires). If the house is situated at (2,4) , bank at (5,8), school at (13,14) and office at (13, 26) and coordinates are in kilometers.

Answer:

Given: House ( 2, 4) , Bank ( 5, 8) , School ( 13, 14) , Office (13, 26)

Distance from House to Office = \sqrt{(13-2)^2 + (26-4)^2} = \sqrt{121+ 484} = \sqrt{605} = 24.6 km

Distance of House to Bank = \sqrt{(5-2)^2 + ( 8-4)^2} = \sqrt{9+16} = 5 km

Distance of Bank to School = \sqrt{(13-5)^2+ (14-8)^2} = \sqrt{64+36} = 10 km

Distance from school to office = \sqrt{(13-13)^2 + (26-14)^2} = \sqrt{144} = 12 km

Therefore total distance traveled = 5 + 10 + 12 = 27  km

Extra distance = 27 - 24.6 = 2.4 km

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Question 54: The center of a circle is (2a, 1) . Find the values of a if the circle passes through the point (11,-a) and has diameter 10\sqrt{2} units.

Answer:

Given: O(2a, 1), A(11, -a)

Radius = 5\sqrt{2}

Therefore (5\sqrt{2})^2 = (11-2a)^2 + ( -a -1)^2

50 = 121 + 4a^2 - 44 a + a^2 +1 + 2a

5a^2 - 42a + 72 = 0

a = 6 \ or \ 2.4

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Question 55: Find a point which is equidistant from the points A(-5,4) and B (-1,6) . How many such points are there?

Answer:

Given: A(-5, 4), B(-1, 6)

Let C(x, y) be equidistant

AC^2 = BC^2

\Rightarrow (x+5)^2 + ( y-4)^2 = (x+1)^2 + ( y - 6)^2

\Rightarrow x^2 + 25 + 10x + y^2 + 16 - 8y = x^2 + 1 + 2x + y^2 + 36 - 12y

\Rightarrow 41+ 10x - 8y = 37 + 2x - 12y

\Rightarrow 8x + 4y = -4

\Rightarrow 2x + y + 1 = 0    … … … … … i)

Therefore all points satisfying the equation i) will be equidistant from the two given points. Hence we have infinite such points.

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Question 56: The points A (2,9), B (a,5) and C (5, 5) are the vertices of a \triangle ABC right angled at B . Find the values of a and hence the area of \triangle ABC .

Answer:

Given: A(2, 9), B(a, 5), C(5, 5)

AB^2 = ( a-2)^2 + (5-9)^2 = (a-2)^2 + 16

BC^2 = ( 5-a)^2 + (5-5)^2 = (5-a)^2

AC^2 = ( 2-5)^2 + (9-5)^2 = 9 + 16 = 25

AB^2 + BC^2 = AC^2

\Rightarrow (a-2)^2 + 16 + (5-a)^2 = 25

\Rightarrow a^2 + 4 - 4a + 16 + 25 + a^2 - 10a = 25

\Rightarrow 2a^2 - 14a + 20 = 0

\Rightarrow a^2 - 7a + 10 = 0

\Rightarrow ( a-5)(a-2) = 0

\Rightarrow a = 5 \ or \ 2

When a = 5, AB^2 = 25 and BC^2 = 0. BC \neq 0 hence a \neq 5

When a = 2, AB^2 = 16 and BC^2 = 9 . Hence a = 2

Therefore Area = \frac{1}{2} \times 4 \times 3 = 6 sq units.

Link to the start of Exercise 19.4