Question

数学微积分题目，题目如下

A man starts walking north at 6 ft/s from a point P. Five minutes later, a woman starts walking south at 4 ft/s from a point 470 ft due east of P. At what rate ( in ft/s ) are the people moving apart 15 min after the woman starts walking? Please round your answer to the nearest hundredth

Answer 1

题目要求女人出发15min中两人相距距离增加的速率，只要求出两人距离关于时间的函数，然后求微分就可以求得。而两人距离y^2=470^2+(6*5*60+6t+4t)^2
即y=根号下(470^2+(1800+10t)^2)，然后求微分，再把t=15*60=900代入，得到的值精确到100ft/s。
思路就是这样，计算你应该可以完成的吧？

Answer 2

Could you tell some details,i can't understand the problem.may be you can wrote it again by chinese.

Answer 3

maybe he also does not undersand exactly.so he asks for help.