Question

Решите пожалуйста с решением

Answer 1

cos2a = cos²a-sin²a

cos²a = 0.2² = 0.04

sin²a=1-cos²a = 1-0.04 = 0.96

cos2a = cos²a-sin²a = 0.04-0.96 = -0.92

7cos2a = -0.92*7 = -6.44