91Ó°ÊÓ

The differential equation is $\mathrm{y}\text{'}\text{'}-\mathrm{y}=\frac{1}{\mathrm{t}}$.

The homogenous equation is ${\mathrm{r}}^2-1=0$.

Two independent solutions are $\mathrm{r}=Â\pm 1$.

Then${\mathrm{y}}_1={\mathrm{e}}^{\mathrm{t}},{\mathrm{y}}_2={\mathrm{te}}^{-\mathrm{t}}$

${\mathrm{y}}_{\mathrm{h}}\left(\mathrm{t}\right)={\mathrm{c}}_1{\mathrm{e}}^{\mathrm{t}}+{\mathrm{c}}_2{\mathrm{e}}^{-\mathrm{t}}$

The particular solution is ${\mathrm{y}}_{\mathrm{p}}={\mathrm{v}}_1\left(\mathrm{t}\right){\mathrm{e}}^{\mathrm{t}}+{\mathrm{v}}_2\left(\mathrm{t}\right)\mathrm{t}{\mathrm{e}}^{-\mathrm{t}}$.

Here${\mathrm{y}}_{\mathrm{p}}={\mathrm{v}}_1\left(\mathrm{t}\right){\mathrm{e}}^{\mathrm{t}}+{\mathrm{v}}_2\left(\mathrm{t}\right)\mathrm{t}{\mathrm{e}}^{-\mathrm{t}}$

And referring to (9) and solve the system then

$$\begin{gathered} {\mathrm{v}}_1\text{'}{\mathrm{e}}^{\mathrm{t}}+{\mathrm{v}}_2\text{'}{\mathrm{e}}^{-\mathrm{t}}=0 \\ {\mathrm{v}}_1\text{'}{\mathrm{e}}^{\mathrm{t}}-\mathrm{v}{\text{'}}_2{\mathrm{e}}^{-\mathrm{t}}=\frac{\mathrm{f}}{\mathrm{a}} \\ {\mathrm{v}}_1\text{'}{\mathrm{e}}^{\mathrm{t}}-\mathrm{v}{\text{'}}_2{\mathrm{e}}^{-\mathrm{t}}=\frac{1}{\mathrm{t}} \end{gathered}$$

$\begin{array}{rcl}{\mathrm{v}}_1\text{'}& =& \frac{-\mathrm{f}\left(\mathrm{t}\right){\mathrm{y}}_2\left(\mathrm{t}\right)}{\mathrm{a}\left[{\mathrm{y}}_1\left(\mathrm{t}\right)\mathrm{y}{\text{'}}_2\left(\mathrm{t}\right)-\mathrm{y}{\text{'}}_1\left(\mathrm{t}\right){\mathrm{y}}_2\left(\mathrm{t}\right)\right]}\\ & =& \frac{-(\frac{1}{\mathrm{t}}).{\mathrm{e}}^{-\mathrm{t}}}{\left[{\mathrm{e}}^{\mathrm{t}}.(-{\mathrm{e}}^{-\mathrm{t}})-{\mathrm{e}}^{\mathrm{t}}.{\mathrm{e}}^{-\mathrm{t}}\right]}\\ & =& \frac{-(\frac{1}{\mathrm{t}}).{\mathrm{e}}^{-\mathrm{t}}}{-2}\\ & =& \frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\end{array}$

Now integrating this.

${\mathrm{v}}_1\left(\mathrm{t}\right)=∫\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}$

$\begin{array}{rcl}{\mathrm{v}}_2\text{'}& =& \frac{\mathrm{f}\left(\mathrm{t}\right){\mathrm{y}}_1\left(\mathrm{t}\right)}{\mathrm{a}\left[{\mathrm{y}}_1\left(\mathrm{t}\right)\mathrm{y}{\text{'}}_2\left(\mathrm{t}\right)-\mathrm{y}{\text{'}}_1\left(\mathrm{t}\right){\mathrm{y}}_2\left(\mathrm{t}\right)\right]}\\ & =& \frac{\left(\frac{1}{\mathrm{t}}\right).{\mathrm{e}}^{\mathrm{t}}}{\left[{\mathrm{e}}^{\mathrm{t}}.(-{\mathrm{e}}^{-\mathrm{t}})-{\mathrm{e}}^{\mathrm{t}}.{\mathrm{e}}^{-\mathrm{t}}\right]}\\ & =& \frac{\left(\frac{1}{\mathrm{t}}\right).{\mathrm{e}}^{-\mathrm{t}}}{-2}\\ & =& -\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\end{array}$

Integrate this.

${\mathrm{y}}_2\left(\mathrm{t}\right)=∫-\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}$

Thus, a particular solution is:

${\mathrm{y}}_{\mathrm{p}}=\left(∫\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{\mathrm{t}}+\left(∫-\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{-\mathrm{t}}$

And the general solution is:

$$\begin{gathered} \mathrm{y}\left(\mathrm{t}\right)={\mathrm{y}}_{\mathrm{h}}\left(\mathrm{t}\right)+{\mathrm{y}}_{\mathrm{p}}\left(\mathrm{t}\right) \\ \mathrm{y}\left(\mathrm{t}\right)={\mathrm{c}}_1{\mathrm{e}}^{\mathrm{t}}+{\mathrm{c}}_2{\mathrm{e}}^{-\mathrm{t}}+\left(∫\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{\mathrm{t}}+\left(∫-\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{-\mathrm{t}} \end{gathered}$$

The given initial conditions are.

$\begin{array}{rcl}& & \mathrm{y}\left(1\right)={\mathrm{c}}_1{\mathrm{e}}^1+{\mathrm{c}}_2{\mathrm{e}}^{-1}+\left(∫\frac{{\mathrm{e}}^{-1}}{2}\mathrm{dt}\right){\mathrm{e}}^1+\left(∫-\frac{{\mathrm{e}}^{-1}}{2}\mathrm{dt}\right){\mathrm{e}}^{-1}\\ 0& =& {\mathrm{c}}_1\mathrm{e}+{\mathrm{c}}_2{\mathrm{e}}^{-1}\\ {\mathrm{c}}_2& =& -{\mathrm{c}}_1{\mathrm{e}}^2\end{array}$

And

$$\begin{gathered} \mathrm{y}\text{'}\left(\mathrm{t}\right)={\mathrm{c}}_1{\mathrm{e}}^{\mathrm{t}}-{\mathrm{c}}_2{\mathrm{e}}^{-\mathrm{t}}+\left(∫\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{\mathrm{t}}+\frac{1}{2\mathrm{t}}+\left(∫\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{-\mathrm{t}}-\frac{1}{2\mathrm{t}} \\ \mathrm{y}\text{'}\left(1\right)={\mathrm{c}}_1\mathrm{e}-{\mathrm{c}}_2{\mathrm{e}}^{-1}+\left(∫\frac{{\mathrm{e}}^{-1}}{2}\mathrm{dt}\right)\mathrm{e}+\frac{1}{2}+\left(∫\frac{{\mathrm{e}}^{-1}}{2}\mathrm{dt}\right){\mathrm{e}}^{-1}-\frac{1}{2} \\ -2={\mathrm{c}}_1\mathrm{e}-{\mathrm{c}}_2{\mathrm{e}}^{-1} \end{gathered}$$

Solving for ${\mathrm{c}}_1 \mathrm{and} {\mathrm{c}}_2$.

${\mathrm{c}}_1=-\frac{1}{\mathrm{e}} \mathrm{and} {\mathrm{c}}_2=\mathrm{e}$

There for the solution is $\mathrm{y}\left(\mathrm{t}\right)={\mathrm{e}}^{1-\mathrm{t}}-{\mathrm{e}}^{\mathrm{t}-1}+\left(∫\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{\mathrm{t}}+\left(∫-\frac{{\mathrm{e}}^{-\mathrm{t}}}{2\mathrm{t}}\mathrm{dt}\right){\mathrm{e}}^{-\mathrm{t}}$.

And

$\begin{array}{rcl}& & \mathrm{y}\left(2\right)={\mathrm{e}}^{1-2}-{\mathrm{e}}^{2-1}+\left(∫\frac{{\mathrm{e}}^{-2}}{2\left(2\right)}\mathrm{dt}\right){\mathrm{e}}^2+\left(∫-\frac{{\mathrm{e}}^{-2}}{2\left(2\right)}\mathrm{dt}\right){\mathrm{e}}^{-2}\\ & =& {\mathrm{e}}^{-1}-\mathrm{e}\\ & =& -1.93\end{array}$

This is the required result.