Hey guys. Just a quick calculus question for you all. Two people start from the same point. One walks east at 3 km/h and the other walks northeast at 2 km/h. How fast is the distance between them changing after 15 min? Ans: 2.125 km/h Here's what I did: dz/dt= 3 km/h dx/dt= 2 km/h dy/dt= ? 2 km/h * 0.25h= 0.5 km = x 3 km/h * 0.25h= 0.75 km= z y= 0.5590 x^2 + y^2 = z^2 2x (dx/dt) + 2y (dy/dt)= 2z (dz/dt) dy/dt= (z (dz/dt) - x (dx/dt))/ y So I put all the numbers in and I get 2.236. ...and that's kind of close to the answer. Anyways, if anyone could point out what I'm doing wrong, it would be much appreciated. Thanks.