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sin20*cos70+sin10*50
人气:477 ℃ 时间:2020-07-10 07:49:06
解答
sin20cos70+sin10sin50
=(sin20)^2-1/2(cos60-cos40)
=(1-cos40)/2-(cos60-cos40)/2
=(1-1/2)/2
=1/4
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