一道数学应用题,用到初级微积分
Aaboutleavesadockat2:00p.mandtravelsduesouthataspeedof20km/h.Anotherboathasbeenheadingdueeastat15km/handreachesthesamedockat3:00p.m.Atwahttimewerethetwoboatsclosesttogether?
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