Question

cos Sin inverse 3 by 5 + Sin inverse 5 by 13

Answer 1

Let a=sin−1(−35).

Then, sina=−35<0. So, a is in the 3rd quadrant or in the 4th.

Accordingly,

cos a = (- or +)(4/5).

Let b=cos−1(35).

Then, cosb=35>0. So, b is in the 1st quadrant or in the 4th.

Accordingly, sin b = +- 4/5#.

Now, the given expression$ = cos ( a + b ) = cos a cos b - sin a sin b#

=(−or+)(45)(35)−(−35)(±45)

=(−or+)(1225)±1225

=0,±2425