Question

cos(x/4 - α)=12/13,α∈(0,π/4),求(cos2α)/[sin(π/4 + α)]

Answer 1

sin(π/4 + α)

=cos[π/2-(π/4 + α)]

=cos(π/4-α)=12/13

sin²(π/4-α)+cos²(π/4-α)=1

0