Question

1. Find sin(a - b) if sin(a)= 5/13 where a is in the second quadrant and cos(b)= -7/25 where b is in the third quadrant.

2. Find cos(a + b) if sin(a)= 8/17 where a is in the first quadrant and tan(b)= -7/24 where b is in the second quadrant.

Please explain. Thank you!