f′(x)=(sinx)′x-sinx•x′x2=xcosx-sinxx2
故答案为xcosx-sinxx2
― May I take your order now?
―_________
― OK, I'll come back in a few minutes. [ ]
A. No, we need more time.
B. Could you bring us the bill?
C. Yes, here it is. Thank you.
D. Sure, we'd love to.
设圆x2+y2-4x-5=0的弦AB的中点P（3，-1），则直线AB的方程为______过原点的直线与圆x2+y2-2x-4y-4=0相交所得的弦长为4，则该直线的方程为______．
