问一道ap微积分问题求解If one leg AB of a right triangle increases at t

问一道ap微积分问题求解
If one leg AB of a right triangle increases at the rate of 2 inches per second,while the other leg AC decreases at3 inches per second,find how fast the hypotenuse is changing when AB=6 feet and AC=8 feet.
我看的巴郎上的一道例题 他下面写 AB=u du/dt=1/6(ft/sec) AC=v dv/dt=-1/4