A balloon is rising at a constant speed of 5 ft/s. A boy is cycling along a straight road at a constant speed of 15 ft/s. When he passes under the balloon it is 45 ft above him. How fast is the distance between the boy and the balloon ^^^^^^^^^^^^^^^^^^^^^^^^一整个不知道在问什麽!? increasing 3 seconds later? 这题是要问三秒後的距离吗!? 如果是的话...这应该是国中的题目吧... 还是说... 是要问他们之间距离增加的速率(ds/dt)?? 如果是这样的话... 我算的答案是 13 ft/s ~~ 这答案对吗!? ※ 编辑: ahongyeh 来自: 219.68.186.165 (06/16 16:54)