Making a Function Continuous In Exercises $59-64,$ find the constant $a,$ or the constants $a$ and $b$ such that the function is continuous on the entire real number line.
$$f(x)=\left\{\begin{array}{ll}{x^{3},} & {x \leq 2} \\ {a x^{2},} & {x>2}\end{array}\right.$$