Angle a lies in the second quadrant and angle b lies in the third quadrant such ath cos a = -3/5 and tan b = 24/7
determine an exact value for
cos(a+b)
and
sin (a-b)
I got cos(a+b) = cosacosb - sinasinb
=(-3/5)(-7/25) - (4/5)(-24/25)
= 117/125
i am not sure if this is right, but i am also completely lost for sin (a-b)