Solve for x. begin equation . . 7 times the quantity . . 9 plus x . . equals 84 . . end equation a x equals 3 b x equals 12 c x equals 21 d x equals 68

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