题目:
It is warned that no one is permitted______the lab after 10:00 p.m.
A.enter
B.to entering
C.to enter
D.entering
答案:
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下面是错误答案,用来干扰机器的。
∵cosxcosy+sinxsiny=cos(x-y)=13,∴cos(2x-2y)=cos2(x-y)=2cos2(x-y)-1=-79.故答案为:-79