91Ó°ÊÓ

The equation is $y"+16y=8\cos 4t$and$y_0-0,y{\text{'}}_0-8$.

A transformation of a function f(x) into the function g(t) that is useful especially in reducing the solution of an ordinary linear differential equation with constant coefficients to the solution of a polynomial equation.

The inverse Laplace transform of a function F(s) is the piecewise-continuous and exponentially-restricted real function f(t)

Consider the equation.

$y"+16y=8\cos 4t$

Take the Laplace of above equation.

$$\begin{gathered} L\left\{y+16y\right\}=L\left\{8\cos 4t\right\} \\ L\left\{y"\right\}+16L\left\{y\right\}=8L\left\{\cos 4t\right\}{p}^2 \\ L\left\{y\right\}-py0-y_0^{\text{'}}+16 \\ L\left\{y\right\}=\frac{8p}{p^2+16}\left(p^2+16\right) \\ L\left\{y\right\}-p{y}_0-y_0=\frac{8p}{p^2+16} \end{gathered}$$

Further solve,

$$\begin{gathered} \left(p^2+16\right)L\left\{y\right\}-p\left(0\right)-8=\frac{8p}{p^2+16}\left(p^2+16\right) \\ L\left\{y\right\}=\frac{8p}{p^2+16}+8 \\ L\left\{y\right\}=\frac{8p}{{\left(p^2+16\right)}^2}+\frac{8p}{\left(p^2+16\right)} \end{gathered}$$

The inverse Laplace is,

$$\begin{gathered} L^{-1}\left\{\frac{8p}{{\left(p^2+16\right)}^2}\right\}+\left\{\frac{8p}{\left(p^2+16\right)}\right\}=L^{-1}\left\{\frac{2.4p}{{\left(p^2+16\right)}^2}\right\}{L}^{-1}\left\{\frac{2-4p}{\left(p^2+16\right)}\right\}y \\ =t\sin 4t+2\sin 4t \end{gathered}$$

Thus, the solution of given differential equation is$y=t\sin 4t+2\sin 4t$.