Rearranging Formulae Where Subject Appears Twice

Rearranging Formulae Where Subject Appears Twice | Algebra | Maths | FuseSchool

In this video we are going to look at how to change the subject of a formula, when the subject appears twice. We have already looked at how to change the subject in another video, so you may want to watch that first. We always use opposites: adding and subtracting, multiplying and dividing, squaring and square rooting. To keep equations balanced, you must do everything to BOTH sides and then cancel on the one side. Take the rearranging step by step, starting with the things that are ‘least’ connected to your chosen subject. When the subject appears twice in the formula, we need to factorise. E.g. Make x the subject of A = 2xy + xz. Factorise the right hand side to get A = x(2y + z) and then divide both sides by the bracket (2 + z), giving A / (2y + z) = x. Another example: make m the subject of F = (mv - mu) / t. Again, because 'm' appears twice we know we’ll probably need to factorise at some point. Start by moving the ‘t’ as that’s least connect to the m’s, so multiply both sides by 't'. Ft = mv - mu. Now factorise the right hand side. Ft = m(v - u). Finish off by dividing both sides by the bracket (v - u), giving the final answer Ft / (v - u) = m.