To be honest, I think what you did is totally correct. Does your answer not match the answer key? Do you know what the right answer is?
the problem says:
In a right triangle, if one leg (adjacent to 90o) is 3cm, which is increasing
at the speed of 2cm/second; and another leg is 4cm, which is decreasing at
the speed of 2cm/second. How fast is the hypotenuse changing at this time?
this is what i came up with https://www.dropbox.com/s/eyaw81bvue...2001.54.53.jpg
i know for a fact i messed up somewhere towards the end...can someone please guide me in the right direction? thanks!