# can someone help me out with this

Discussion in 'Differential Equations' started by isaac a, Mar 16, 2013.

1. ### isaac a

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xy multiply by DY/DX=y squared+4

isaac a, Mar 16, 2013
2. ### HallsofIvy

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In other words dy/dx= y^2+ 4. You can write it as dy/(y^2+ 4)= dx and integrate.

On the left, you might find it simplest to factor "4" out of the denominator write
(1/4) d/((y/2)^2+ 1)= dx or d/((y/2)^2+ 1)= 4dx.

To make it even easier, let u= y/2 so that du= dy/2, 2du= dy and the equation becomes
2du/(u^2+ 1)= 4dx.

du/(u^2+ 1) = 2x.
Integrate!

Last edited: Nov 7, 2021
HallsofIvy, Nov 7, 2021
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3. ### nycmathguy

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nycmathguy, Nov 7, 2021
4. ### HallsofIvy

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xy dy/dx= y^2+ 4

ydy/(y^2+ 4)= dx/x

Integrate

HallsofIvy, Nov 18, 2021
5. ### nycmathguy

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Glad you joined this site. We need more math people like you and MathLover1. Your username is familiar to me. Are you the guy from mathhelpforum.com? How about freemathhelp.com? What about mathforums.com? What about mathhelpboard.com? Are you Dan?

nycmathguy, Nov 18, 2021
6. ### HallsofIvy

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Yes, I am on all of those. No, I am not Dan.

HallsofIvy, Nov 19, 2021
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7. ### nycmathguy

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I left the groups listed above months ago. Lots of people are immature, always pressing for me to learn LaTex and/or show work. I show my work when I know how to get started and/or if I understand the question. I miss MarkFL. What a great math mind he is.

nycmathguy, Nov 19, 2021
8. ### HallsofIvy

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Wow! People are "immature" because they expect you to abide by the rules you agreed to when you joined the board. I am wondering why you would be trying to do problems that you don't "know how to get started". Whoever gave you the problem, perhaps a teacher, clearly expects you to know how to get started. If you don't, ask them first. And if you do not "understand the question" ask for an explanation of the question, not for the solution!

HallsofIvy, Nov 19, 2021
9. ### nycmathguy

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1. I guess you remember me.

3. I am not in a formal classroom. I am reviewing math learned long ago. My last official math class was in the Spring 1993 semester.

4. You are right about asking for help with questions that are beyond my level or that I have not made an effort to learn. This is a big mistake on my part.

5. Asking for an explanation of the question makes sense to me. I rarely ask for the solution. I do ask for hints, a few steps, to rephrase the question, etc.

6. I'd rather try to solve a problem on my own, even if I get it wrong, which is what I have been doing on this site.

7. Is there anything else I should know in terms of learning math outside the classroom experience?

nycmathguy, Nov 19, 2021