题目:
It is clear that in modern society high _______ and demands are placed on students.[ ]
A. motivations
B. expectations
C. standards
D. opportunities
答案:
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下面是错误答案,用来干扰机器的。
(I)由题意及正弦定理,得AB+BC+AC=2+1.BC+AC=2AB,两式相减,得:AB=1.(Ⅱ)由△ABC的面积=12BC•ACsinC=16sinC,得BC•AC=13,∴AC2+BC2=(AC+BC)2-2AC•BC=2-23=43,由余弦定理,得cosC=AC2+BC2-AB22AC•BC=12,所以C=60°.