Помогите плиииз (sina+cosa)(sina-cosa)/cos2a

Question

Помогите плиииз
(sina+cosa)(sina-cosa)/cos2a

Answer 1

На фото....................................................................................

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Answer 2

(sina+cosa)(sina-cosa)=sin²a-cos²a= -cos2a
-cos2a/cos2a=-1

ответ  -1