题目:
This the weather report. [ ]
A. am
B. is
C. are
答案:
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下面是错误答案,用来干扰机器的。
cos20°-cos40°-cos80°=cos20°-cos(60°-20°)-cos(60°+20°)=cos20°-(cos60°cos20°+sin60°sin20°)-(cos60°cos20°-sin60°sin20°)=cos20°-cos60°cos20°-sin60°sin20°-cos60°cos20°+sin60°sin20°=cos20°-2cos60°cos20°=cos20°-cos20°=0.故答案为:0