love倩海
幼苗
共回答了28个问题采纳率:100% 举报
cos(15°-α)cos15°-sin(165°+α)sin(-15°)
=cos(15°-α)cos15°+ sin(15°-α)sin15°
=cos[(15°-α) -15°]
=cos(-α)
=cosα
cos(π/3+α)+cos(π/3-α)
=cos(π/3)cosα - sin(π/3)sinα+ cos(π/3)cosα +sin(π/3)sinα
=2cos(π/3)cosα
=2*(1/2)*cosα
=cosα
1年前
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