Question

Sabendo que sen a = 15/17 com 0 < a < π/2, calcular cos 2a:

a) 161/289

b) - 161/289

c) 23/17

d) 7/17

e) - 7/17

Answer 1

Resposta:

cós 2a = cos^2 a - sin^2 a = 1 - 2sin^2 a = 1- 2(15/17)^2 = (289-2*225)/289 = -161/289 (b)