Section 3:
TRANSPOSITION OF FORMULAE

 

A formula is a rule, usually written using mathematical symbols, which shows how two or more variables are related.

Some formulae are explicit, i.e. they spell the relation out with no ambiguity. For example,

is the formula for the area of a rectangle.
It tells you clearly that if you know the length ( ) and the breadth ( )
you have to multiply them together to get the area.

Other formulae are implicit, i.e. they imply the relationship without spelling it out. For example


is a formula which relates the rotational speed (N) and the number of teeth (n) for two interlocked gear wheels A and B.

When we transpose (or change the subject of) a formula we rearrange it so that a different variable is on its own on one side of the formula. That variable becomes the subject of the formula.