Abird (b) is spotted flying 6,000 feet from a tower ( an observer (o) spots the top of the tower (t) at a distance of 9,000 feet. what is the angle of depression from the bird (b) to the observer (o)?

Which sum or difference identity would you use to verify that cos (180° - q) = -cos q? a.) sin (a -b) = sin a cos b – cos a sin b b.) cos (a -b) = cos a cos b – sin a sin b c.) cos (a -b) = cos a cosb + sin a sin b d.) sin (a + b) = sin a cos b + cos a sin b