A passenger plane made a trip to Moscow and back. The trip there took five hours and the trip back took eight hours. It averaged 170 mph on the return trip. Find the average
speed of the trip there.

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