Some questions I need help with, out of a selection of others. I've tried them, and have been scribbling all over my notepads, and just can't get it! I hope if someone helps with part a) for both of these questions, I'll be able to do b) c) and d) myself. Thanks! One of the main things i don't get in the second question is how cos(theta)= 2/3 in quadrant 4... I'm kind of new to this Math, but haven't had trouble so far with any previous questions leading up to this. And for the 1st question, I tried to find cos(x) and cos(y), then substituting into sin(x+y)=sin(x)cos(y)+sin(y)cos(x)... Apparently giving me the wrong answer (these questions are marked online, so maybe my syntax is wrong, but I'd also appreciate if anyone could check my answer/teach me how to do it...)

My answer for 1. (i think wrong): (-(sqrt(7))/8)+(3(sqrt(3))/8)

for 2: (i think wrong): 4(sqrt(5))/9

Not sure if u can see pics/questions..