hi, ive been stuck on this question for days, any help would be appreciated.

a pendulum that is 48cm long has swung through an angle of x. starting from vertical it is 8cm higher than lower position. how much higher would it be after going through an angle of 2x.

we can not use a calculator (that would be slightly easy) and a hint has been given to use a cos identity. cos2x=2cos^2x-1

im not after the answer, just a point in the right direction as its been driving me insane, thanks in advance