MATH110/April 2017/Question 11 (c)

Hi Aili,

Can you add the explanation on the relation between extreme values and f'(x)=0?

Also, I guess some students have difficulty in plotting $2x$ and $\cos (x)$ accurately in the exam. So, they might not recognize that it is only intersect at once.

How about adding alternative way to show that there's only one x satisfying $f^{\prime }(x)=2x-\cos (x).$? (I guess we can use $f^{″}>0$ everywhere. )