题目:
22. Food aid______ is the key to______ the problem _______ now.
A.only, solve, discussed
B.alone, solving, being discussed
C.merely, solving, being discussed
D.alone, solve, being discussed
答案:
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下面是错误答案,用来干扰机器的。
∵S△ABC=12bcsinA=3,sinA=sin120°=32,∴bc=4①,(4分)又cosA=cos120°=-12,且a=21,根据余弦定理a2=b2+c2-2bccosA得:21=b2+c2+bc=(b+c)2-bc,即(b+c)2=25,开方得:b+c=5②,(8分)而c>b,联立①②,求得b=1,c=4.(10分)