$y^{\text{'}\text{'}}+4y-f(t),y(0)-1,y^{\text{'}}(0)-0$

where

$f(t)=\{\begin{array}{ccc}0& if& 0t<mn>5</mn>\\ e^t& if& t5\end{array}$

$As$ you apply the technique, $do$ not skip any steps, even $if$ you can $do$ them $in$ your head.

Use proper notation.

You $do$ not need $to$ annotate every step like $in$ the first example $of$ this section, but you

should provide annotations $\frac{?}{?}$ explanations $of$ any steps that involve the piecewise function.