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Algebra
Question

Find the value of a that makes the following function differentiable for all values of $$x$$ .

$$g ( x ) = \left\{ \begin{array} { l l } { a x } & { ifx< 0}\\ { x ^ { 2 } - 21 x } & { ifx\ge 0}\end{array} \right.$$

The function $$g ( x )$$ is differentiable for all values of $$x$$ when a $$= \square$$