2sin15° cos15°/cos2 67,5°- sin2 67,5°

Question

2sin15° cos15°/cos2 67,5°- sin2 67,5°

Answer 1

2sinxcosx=sin2x
cos²y-sin²y=cos2y
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2sin15cos15/(cos²67,5-sin67,5)=sin30/cos135=sin30/cos(180-45)=
=sin30/(-cos45)=1/2:(-√2/2)=1/2*(-√2)=-1/√2