# Assignment 4

Common Mistakes:

• In problem 5, some students forgot to write down the equation of the tangent line after they got the slope of it. Also there are students who forgot to write down the smallest value of the slope of the tangent line after they figured out when it reaches the minimum.
• In problem 8, you should use implicit differentiation directly. Most students used $\cos x=\sqrt{1-\sin^2 x}$. But this is not true, since $\cos x$ can be $-\sqrt{1-sin^2 x}$ as well.