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Find the $a$ that makes $f(x)$ continuous for all real numbers.

$$f(x)=\begin{Bmatrix} \frac { sin(2x) }{ x } +a & x<0 \\\ 3cos(x) & 0\le x \end{Bmatrix}$$

$a=0$

$a=1$

$a=3$

No value of $a$ can make $f(x)$ continuous.