Rearranging Formulae

Things to remember: Don’t rush it. You must go through each stage of your method and not try to skip any. If you are making x the subject it means that you want to end up with x= and this is the only x in your answer. Whatever you do to one side of the equals sign you must do to the other.

Example Rearrange the formula a = x +.to make x the subject. Method - multiply both sides by d rearrange to get x’s on the left factorise divide by (d + c) a = x + ad = dx + cx dx + cx = ad x(d + c) = ad x =

Example Rearrange the formula a = +.to make p the subject. Method - multiply both sides by pq rearrange to get p’s on the left factorise divide by (aq – 1) a = + apq = q + p apq – p = q p(aq – 1) = q p =

Example Rearrange the formula a = b +.to make p the subject. Method - multiply both sides by 1 + p expand brackets rearrange to get p’s on the left divide by (a – b) a = b + a(1 + p) = b(1 + p) + c a + ap = b + bp + c ap – bp = b + c – a p = p(a – b) = b + c – a factorise

Example Rearrange the formula s = b +.to make t the subject. Method - subtract b from both sides square both sides rearrange to get t on the left multiply by p s = b + s – b = (s – b)² = = (s – b)² t = p(s – b)²