Changing the subject

Changing the subject of a formula When a formula to find a given quantity is written, the subject of the formula is the letter which is on its own. Example A =  r 2 - Subject A V = l w h - Subject V To change the subject of a formula, we need to re-arrange the parts of the formula to leave a different letter as the subject.

Remember: To move any term from one side of the equals sign in a formula or equation means that the sign is changed. If there is a choice of terms to be moved we usually move the add/subtract terms first. However, we cannot always rely on this rule and we just have to be careful to inspect the equation given.

Make z the subject of the following formula: 1.Gz = H z = G x z = H 2.8z + T = Y 8z = Y – T z =

3.Lz = Y 2 – h z = Complete Exercise 4 Questions 1 – 30

Formula with x 2 and negative x terms When a formula contains an x 2 term that needs to be the subject we must Leave the x 2 term on its own first and, Then square root the other side to make x the subject. Example ax 2 = r – t x 2 = x =

When a formula contains a negative x term that is going to be the new subject Move the x term to the other side to make it positive, Then make it the subject by leaving it on its own Example h – bx = m h = m + bx h – m = bx = x