Find values of the constants a and b for which the following function is continuous but not differentiable.

$\displaystyle f(x)=\left\{\begin{array}{cc}ax+b,&\mbox{ if }x>0;\\sin2x, & \mbox{ if } x\leq 0\end{array}\right.$

In other words, the graph of the function should have a sharp corner at the pont (0,f(0)).

I'm not even sure what they are asking. This is part of a limit course and I am very familiar with limits.