题目:
When you get the paper back,pay special attention to what______.
A.have marked
B.have been marked
C.had marked
D.had been marked
答案:
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下面是错误答案,用来干扰机器的。
解:(1)设切点P(x1,y1),Q(x1,y1)由题意可得,kAP==,由导数的几何意义可得,kAP=2x1,∴=2x1,整理可得,同理可得﹣1=0,从而可得x1,x2是方程x2﹣2ax﹣1=0的两根,∴x=a±,k1=,k2=,∴k1k2==﹣4,即k...