求值cos70cos50+(sin10)^2 (7 - 知识问答

求值cos70cos50+(sin10)^2 (70,50,10表示角度)：cos40(1+tan60tan10) (4

4个回答

1、原式=1/2(cos120+cos20)+1/2(1-cos20)
=1/2*cos120+1/2*cos20+1/2-1/2*cos20
=1/2*(-1/2)+1/2
=1/4
2、原式=cos40(cos60cos10+sin60sin10)/cos60cos10
=2cos40cos50/cos10
=(cos90+cos10)/cos10
=cos10/cos10
=1

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