Find the values of a and b that make f continuous everywhere. f(x)=\left\{\begin{array}{ll} \frac{x^{2}-4}{x-2} & \text { if } x<2 \\ a x^{2}-b x+3 & \text { if } 2

\leq x<3 \\ 2 x-a+b & \text { if } x \geq 3 \end{array}\right.