# Math Help - Addition formulae

With question 1 I have guessed the unknown side lengths using common pythagorean triples. Is there another way to get them?

I have done 2a. Can I have a clue for 2b? I expect it uses addition formulae.

2. Originally Posted by Stuck Man
With question 1 I have guessed the unknown side lengths using common pythagorean triples. Is there another way to get them?

I have done 2a. Can I have a clue for 2b? I expect it uses addition formulae.
2(b) can be calculated using $Sin(A-B)=SinACosB-CosASinB$

given that $A=180^o$ and $B=2x$

and $Sin180^0=0$ and $Cos180^o=-1$

3. Thanks. I copied the diagram for question 1 and missed the length of QP so theres no need to reply to that now.