Gr12 Calculus Help [Challenging]

I had an assignment for calculus and there are these 3 questions that keep irritating me. I have answered all of them but deleted the answers so I could get different ideas from others just incase I am wrong. The triangle one was the hardest to solve out of all of them. If you want to put your calculus skills to the test and also help me out at the same time, attempt these questions :biggrin:

Here are the 3 questions that gave me the most trouble, arranged from easiest to hardest:

1) http://i.imgur.com/N8d2Wjt.jpg

2) http://i.imgur.com/l1avIzg.jpg

3) http://i.imgur.com/UfdnQjW.jpg

 

Gravedug, but what the hell. First one is a similar shape to y = -x^2. I obviously can't sketch it. (Just take the derivative of the function which looks like -x^3. I'm leaving out constants and stretches because the function isn't actually -x^3.

Second one:
Just chain rule. (f(g(x)))' = g'(x)f'(g(x)). Don't want to do this out, but just put in g(x) for u's in f'(u), and multiply it by g'(x).

Last one:
Find an explicit formula for the area in terms of the side length, and in terms of time. (Shouldn't be difficult.). Differentiate the time one. Find side length when area is 100. (Again, just solve for x from the non-differentiated formula). plug in side length into differentiated formula. Boom done.