Determine the value of constant involved in the definition so that the given function is continuous: f(x)=k(x2+3x), if x<0cos 2x,if x≥0

Determine the value of constant involved in the definition so that the given function is continuous: $f (x) = \{\begin{cases} k (x^{2} + 3 x) & , i f x < 0 \\ \cos 2 x & , i f x \geq 0 \end{cases}$

Match the items on the right to the items on the left.