# Thread: Graph of differential equations?

1. ## Graph of differential equations?

I have this question: Is my answer correct? I came to this answer because I actually worked each out to find c1 and then graphed them. When I graphed the second one y became negative while x, (t), went to infinity. This is an electronic version of this graph: Oh, and I found that c1 for option 2 was (-8.46). The other options didn't turn out like this for their graph, but it could've been a mistake in a number of different steps. Is my answer right? Thanks!

2. ## Re: Graph of differential equations?

no that's not correct

3. ## Re: Graph of differential equations?

Originally Posted by romsek
no that's not correct
Could you tell me why it's not correct?

4. ## Re: Graph of differential equations?

Originally Posted by canyouhelp
Could you tell me why it's not correct?

it doesn't exhibit the desired behavior

5. ## Re: Graph of differential equations?

If $k<0$, then as $t \to \infty$, $y \to a$.
If $k>0$, then as $t \to \infty$, $e^{kt} \to \infty$, so if you want $y \to -\infty$, you need $Ae^{kt} \to -\infty$, so $A<0$. Which of the choices offers $k>0$ and $A<0$? As the problem says, you must solve for $A$ in each case.

6. ## Re: Graph of differential equations?

Originally Posted by romsek

it doesn't exhibit the desired behavior
Okay, then I believe option 4 is right?

7. ## Re: Graph of differential equations?

Originally Posted by canyouhelp
Okay, then I believe option 4 is right?
yes

8. ## Re: Graph of differential equations?

Originally Posted by canyouhelp
Okay, then I believe option 4 is right?
Correct.