已知cos(2a-π/4)=1/3则sin(a-π/8)=
问题描述：
已知cos(2a-π/4)=1/3则sin(a-π/8)=
答
1/根号3
或-1/根号3
答
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