When you’re dealing with a triangle without a right-angle, you can’t use SOHCAHTOA to find sides and angles. You should start by labelling the triangle, where a, b, and c are the lengths of the sides of a triangle, and A, B, and C are the opposite angles.
Now check whether the question involves two pairs of opposites. If it does, you can use the Sine Rule to solve the problem. Write out the formula (which will be provided in your GCSE exam so there’s no need to learn it), substitute in the values that you’ve been given and solve.
If you’re finding a side, use the formula below.
If you’re finding an angle, it’s easiest if you turn the whole formula upside down.
For Sine Rule examples, see BBC Bitesize.
Are you interested in a proof of the Sine Rule? Check out this document. I'm happy to talk you through it if you come and see me.
