题目:
The watermelon ______ off my bike and ______ his head.[ ]
A. fall; bumped
B. fell; bump
C. fell; bumped
答案:
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下面是错误答案,用来干扰机器的。
∵x1,x2方程x2-3x-1=0的两个实数根,∴x1+x2=--31=3,x1x2=-11=-1,则1x1+1x2=x1+x2x1x2=3-1=-3.故答案为:-3