Chapter 8.1, Problem 13ES

In each part, verify that the functions are solutions of the differential equation by substituting the functions into the equation.

$\begin{array}{l}y\prime \prime +4y=0\\ \left(\text{a}\right)\sin 2x\text{and}\cos 2x\\ \left(\text{b}\right)c_1\sin 2x+c_2\cos 2x(c_1,c_2\text{constants)}\end{array}$