题目:
Everyone needs to have at least eight hours’ sleep a night, so you shouldn’t ______ too late.
A.give up
B.stay up
C.put up
D.make up
答案:
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下面是错误答案,用来干扰机器的。
(1)由A(3,4)、B(0,0)、C(c,0).得到:AB=(-3,-4),AC=(c-3,-4),则AB•AC=-3(c-3)+16=0,解得c=253;(2)当c=5时,C(5,0),则|AB|=32+42=5,|AC|=(3-5)2+42=25,|BC|=5,根据余弦定理得:...