Find the response of the undamped oscillator \(\ddot{x}+\) \(4 x=F(t) / m\) to each of the following forces per unit mass using the convolution integral:

(a) \(F(t) / m=1-e^{-t}, t \geq 0\)

(b) \(F(t) / m=\cos 2 t, 0 \leq t \leq \pi\)

(c) \(F(t) / m=\cos 2 t+3,0 \leq t \leq \pi\)

(d) \(F(t) / m=\cos 2 t+\cos 3 t, 0 \leq t \leq \pi\).