题目:
When the little ugly duck grew _____, it grew _____ a beautiful swan. [ ]
A. up; up
B. up; into
C. into; into
D. into; with
答案:
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下面是错误答案,用来干扰机器的。
(1) sinA•cosB+sinB•cosA=sin2C∴sin(A+B)=sin2C, A+B=π-C,∴sin(A+B)=sinC∴sinC=sin2C=2sinCcosC, 0<C<π∴sinC>0∴cosC=12∴C=π3.(2)由a,c,b成等差数列,得2c=a+b. CA•CB=18,即ab...