1. Trig - Cosine

Explain why cos85 + cos95 = 0.

--> cos 85 degrees + cos 95 degrees = 0.

Thank you

2. consider the problem as

$\cos(90-5)+\cos(90+5)$

use the compound angle identity keeping in mind that $\cos(90) = 0$

3. they cancel out to zero

if you think about where 90degrees is
you will see that the cos beween 0 to 90 (85) is the same length as the cos from 90 to 180 (95) just 5 degrees both sides of off 90degrees however in the I quadarent
the cos is positive and in the II quadarant the cos neg so they cancel out to zero