Formula: A formula is nothing but a relation between two or more variables.

Subject of Formula: The subject of a formula is a variable which is expressed in terms of other variables.

Some commonly used formulas are:

 Perimeter of a square of side (a): $P=4a$ $P=4a$ Area of a square of side (a): $A = a^2$ $A = a^2$  Volume of a cube of side (a): $A = a^3$ $A = a^3$  Perimeter rectangle of width ( w ) and length (l): $P = 2w + 2l$ $P = 2w + 2l$ Area of a rectangle of width ( w ) and length (l): $A=w\times l$ $A=w\times l$  Volume of a cuboid of width (a), length (b) & height (h): $A = a\times b\times h$ $A = a\times b\times h$  Circumference of a circle of radius (r): $C = 2 \pi r$ $C = 2 \pi r$ Area of a circle of radius (r): $A = \pi r^2$ $A = \pi r^2$  Surface area of a sphere of radius (r): $A = 4 \pi r^2$ $A = 4 \pi r^2$ Volume of a sphere of radius (r): $\displaystyle V = \frac{4}{3}\pi r^3$ $\displaystyle V = \frac{4}{3}\pi r^3$  Surface area of a cone of radius (r) and height (h): $A=\pi r (r+\sqrt{h^2+r^2})$ $A=\pi r (r+\sqrt{h^2+r^2})$ Volume of a cone of radius (r) and height (h): $\displaystyle V = \frac{1}{3} \pi r^2 h$ $\displaystyle V = \frac{1}{3} \pi r^2 h$  Surface area of a cylinder of radius (r) and height (h): $A=2 \pi rh+2 \pi r^2$ $A=2 \pi rh+2 \pi r^2$ Volume of a cylinder of radius (r) and height (h): $V=\pi r^2 h$ $V=\pi r^2 h$  But then the formula could be any relation between variables. For example, the newton’s laws of motion as stated below $v=u+at$ $2as=v^2-u^2$ $S = ut+\frac{1}{2} at^2$

or something as simple like $x=2y \ or\ x=a+b$