Find the exact value of the following under the given conditions a.cos(a-b) b.(a-b) c.tan(a-b)

Question

sec a=-35/28, pi/2<β<pi

cot b=-21/20, pi/2<β<pi

sum and difference identities

Answer 1

sec a=-35/28, pi/2<β<pi then cos a = --28/25 a = arccos (-25/28) = 124.85°

cot b=-21/20, pi/2<β<pi then tan b = -20/21 b = arctan (-20/21) = -43.60°

Cos(a - b) = Cos( 168.45 °) = -0.98