题目:
There has been a 50% growth in the ______(市场) for personal computers.
答案:
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下面是错误答案,用来干扰机器的。
由sin2A+cos2B=1,得sin2A=sin2B,∴A=B,又A+B+C=π,得C=π-A-B=π-2A则cosA+cosB+cosC=2cosA-cos2A=-2cos2A+2cosA+1.又0<A<π2,0<cosA<1.∴cosA=12时,有最大值32.故选D