Comment on the statement: The general solution of $\displaystyle \varphi''+6\varphi'+\lambda\varphi=0$ is

$\displaystyle \varphi=C_1\exp(-3+i\sqrt{\lambda-9})+C_2\exp(-3-i\sqrt{\lambda-9})$.

I am not sure what this question wants me to comment about unless it is the fact it should be written like

$\displaystyle \varphi=e^{-3}\left[A\cos(x\sqrt{\lambda-9})+B\sin(x\sqrt{\lambda-9})\right]$