题目内容
cos(70°+α)cos(10°+α)+sin(70°+α)sin(170°-α)=___________.
解析：原式=cos(70°+α)cos(10°+α)+sin(70°+α)sin［180°-(10°+α)］
=cos(70°+α)cos(10°+α)+sin(70°+α)sin(10°+α)
=cos［(70°+α)-(10°+α)］
=cos60°=
.
答案：
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题目内容
cos(70°+α)cos(10°+α)+sin(70°+α)sin(170°-α)=___________.
解析：原式=cos(70°+α)cos(10°+α)+sin(70°+α)sin［180°-(10°+α)］
=cos(70°+α)cos(10°+α)+sin(70°+α)sin(10°+α)
=cos［(70°+α)-(10°+α)］
=cos60°=.
答案：
)＝，其中
，则cos（2α-40°）= ．