The differential equation
$$y^{\prime\prime}-y = 0$$ has one of the following two parameter families as its general solution
$$\begin{aligned} y&=c_1e^x+c_2e^{-x}\\ &&&\\ y&=c_1\cos(x)+c_2\sin(x)\\ &&&\\ y&=c_1\tan(x)+c_2\sec(x)\\ &&&\\ y&=c_1+c_2x\\ \end{aligned}$$
Find the solution such that $y(0) = 3$ and $y^\prime(0)=6$: