Given, $y=f(x) ; \frac{d^{2} y}{d x^{2}}+4 y=0 ; y(0)=0 ; \frac{d y}{d x}(0)=1$. The problem is a/an
- initial value problem having solution $\mathrm{y}=x$
- boundary value problem having solution $\mathrm{y}=x$
- initial value problem having solution $\mathrm{y}=\frac{1}{2} \sin 2 x$
- boundary value problem having solution $\mathrm{y}=\frac{1}{2} \sin 2 x$