How do you go about rearranging equations where the required subject appears on both sides? Such as making x the subject of 7x + a = 3x + b.

  • Google+ icon
  • LinkedIn icon
  • 932 views

To rearrange any equation, you must always do the same to both sides.
If you take a number from one side, you must also take it from the other. If you divide a side by one number you must divide the other by the same number (and this applies to the whole of both sides, not just part of the side).

7x + a = 3x + b, make x the subject:
Begin by collecting like terms on each side (so all the terms involving x on one side, and all the other terms on the other side).
1) Take 3x from both sides:
7x + a - 3x = 3x + b - 3x
4x + a = b
2) Take a from both sides:
4x + a - a = b - a
4x = b - a
3) Divide both sides by 4 (as x must be alone):
(4x)/4 = (b - a)/4
x = (b - a)/4 This is our answer

Rachael T. 11 Plus Maths tutor, GCSE Maths tutor, 13 plus  Maths tuto...

About the author

is an online GCSE Maths tutor with MyTutor studying at Durham University

Still stuck? Get one-to-one help from a personally interviewed subject specialist.

95% of our customers rate us

Browse tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok