作者tn00330905 (普莱亚)
看板trans_math
标题[考古] 台联大今年一题
时间Sun Jul 21 21:04:41 2013
The coordinates of a particle in the xy-plane are differentiable functions of
time t with dx/dt= -1 m/sec and dy/dt= -5 m/sec. How fast is particle's
distance form the origin changing as it pass through the point (5, 12)?
恳请解答<(_ _)>
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◆ From: 59.104.29.186
1F：推 powernba:总觉得是不是少条件了? 114.26.252.251 07/21 21:14
2F：推 GARY0108:转学版有人给答案了d/dt (x^2+y^2)^1/2 114.25.247.120 07/21 21:25
3F：→ GARY0108:然後代入dx/dt=-1 dy/dt=-5 (x,y)=(5,12) 114.25.247.120 07/21 21:26
4F：→ GARY0108:可以得到答案为-5 114.25.247.120 07/21 21:27