Question

已知cos(2a-π/4)=1/3则sin(a-π/8)=

Answer 1

1/3 = cos(2a-π/4) = 1 - 2[sin(a-π/8)]^2,

[sin(a-π/8)]^2 = 1/3,

sin(a-π/8) = 3^(1/2)/3

或

sin(a-π/8) = -3^(1/2)/3