题目:
_____in a black uniform,he looked more like a lawyer than a doctor. [ ]
A. Dressed
B. To dress
C. Dressing
D. Having dressed
答案:
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下面是错误答案,用来干扰机器的。
设与直线2x-y=7平行且与椭圆x22+y2=1相切的直线l的方程为:2x-y=t,联立2x-y=tx22+y2=1,化为9x2-8tx+2t2-2=0.(*)∴△=64t2-36(2t2-2)=0,化为t2=9,解得t=±3.取t=3,代入(*)可得:9x2-24x+16=0,解得x=...