已知sin((π/4)-α)=5/13,(0

问题描述:

已知sin((π/4)-α)=5/13,(0

cos(π/4+α)/cos2α
=√2/2(cosa+sina)/(cos²a-sin²a)
=√2/2(cosa+sina)/[(cosa+sina)(cosa-sina)]
=√2/2*1/(cosa-sina)
sin((π/4)-α)=5/13,(0