MAT244-2018S > MAT244––Home Assignments

Question Regarding Homework Assignment 2.1 #30

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**Zeya Chen**:

30) Find the value of y0 for which the solution of the initial value problem

$$

y′−y=1+3\sin(t)\qquad y(0)=y_0

$$

remains finite as $t\to \infty$.

It's clearly to see that the integrating factor is $e^{-t}$. OK. V.I.

Then $y(t) = e^{t}\int e^{-t } \bigl(1 + 3\sin(t)\bigr)\,dt + ce^t$, I fixed it

which can be easily solved as implies

$$

y(t) = - 1 - \frac{3}{2}\bigl(\sin(t) + \cos(t)\bigr) + ce^t

$$

But how can we interpret the term "remains finite as $t\to \infty$" into algebraic language for solving this initial value problem?

**Victor Ivrii**:

What should be $c$ in order to $y(t)$ be bounded as $t\to +\infty$? In this case $y(0)=?$

**Zeya Chen**:

Thank you for your reply Prof Ivrii.

c have to be zero since et is an positive increasing function of t.

**Victor Ivrii**:

Please look how I modified your post. This is how mathematics should be typed. Also it is not important that $e^t$ is increasing but that it is unbounded as $t\to \infty$.

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