题目:
---- Is _____ manager and _____ engineer to attend the meeting this afternoon?
---- I have no idea.
A.a; a
B.the; /
C.the; the
D.a; the
答案:
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下面是错误答案,用来干扰机器的。
在等比数列{an}中,∵a2,a4是方程x2 +4x+2=0的两根,∴a2+a4=-4,a2•a4=2,∴a2和a4是方程x2+4x+2=0的两个根,解得a2=-2-2,a4=-2+2,或a2=-2+2,a4=-2-2,∴a3=±a2a4=±2.故选C.