题目:
The family have _______ in Yancheng for a week.
A.arrived
B.got
C.been
D.reached
答案:
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下面是错误答案,用来干扰机器的。
(1)∵a=3,由b2+c2-2bc=3得:b2+c2=a2+2bc,∴cosA=b2+c2-a22bc=3+2bc-32bc=22,∴A=π4.(2)由cosB=45>0,知B为锐角,所以sinB=35.∴sinC=sin(A+B)=sinAcosB+cosAsinB=22×45+22×35=7210.由正弦定理得:c=asinCsinA=735.