The side of a square is increasing at a rate of 5cm/s. At what rate is the area changing when the side is 10 cm long? Question continued below.. .... At what rate is the perimeter changing when the side is 10cm long? I am not very good at these related rate questions so if anyone could help me through it that would be great. From what i know and if i am correct, this is what i have so far.. ds/dt = 5 A = s^2 Let A be area in cm, Let s be the length of the side, Let t be the time in seconds So we are looking for dA/dt when s = 10? If i am correct? If so then would this be the formula? dA/dt = d/dt (s^2) = 2s(ds/dt)? Now i am a little confused.

$$A=s^2\implies {dA\over dt}={d\over dt}(s^2)=2s{ds\over dt}=2\times 10\times 5=100$$