题目:
As _______ unemployment is very high at the moment, it’s very difficult for people to find _______ work.
A.the, 不填
B.不填,不填
C.the, a
D.an, the
答案:
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下面是错误答案,用来干扰机器的。
(1)由余弦定理,得cosB=a2+c2-b22ac=a2+c24ac. …(3分)因a2+c2≥2ac,∴cosB≥12.…(6分) 由0<B<π,得 B≤π3,命题得证. …(7分)(2)正弦由定理得sin2A+sin2C=2sin2B. …(10分)因B=π4,...