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 June 3rd, 2012, 01:52 AM #1 Member   Joined: Apr 2012 Posts: 47 Thanks: 0 differential equation use substitution methode for this equation i use substitution methode. but my answer is not right. dont know where i make a mistake, please someone can help me to check. thanks! right answer is y=4x ln(cx) June 3rd, 2012, 02:43 AM #2 Member   Joined: Apr 2012 Posts: 47 Thanks: 0 Re: differential equation use substitution methode i have an other question last step i dont get it, where is u' and +u get from? what is the u'? June 3rd, 2012, 02:50 AM #3 Math Team   Joined: Mar 2012 From: India, West Bengal Posts: 3,871 Thanks: 86 Math Focus: Number Theory Re: differential equation use substitution methode U=Y*1/x+4 x*U-4=Y Its the mistake in your previous question  June 3rd, 2012, 03:05 AM #4 Math Team   Joined: Mar 2012 From: India, West Bengal Posts: 3,871 Thanks: 86 Math Focus: Number Theory Re: differential equation use substitution methode x*y'=y+4*x x*dy=y*dx+4x*dx x*dy-y*dx=4x*dx (x*dy-y*dx)/(x^2) = (4/x)*dx d(y/x) = (4/x)*dx, integrating both sides, y/x+c1 = 4ln(x)+c2 y=4xln(x)+Cx where C=c1-c2 My C = your 4ln(c)  June 3rd, 2012, 03:49 AM   #5
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Re: differential equation use substitution methode

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 Originally Posted by mathbalarka U=Y*1/x+4 x*U-4=Y Its the mistake in your previous question thanks alot mathbalarka for helping me out. do you know this question?

Quote:
 Originally Posted by zell^ i have an other question last step i dont get it, where is u' and +u get from? what is the u'? June 3rd, 2012, 04:03 AM #6 Math Team   Joined: Nov 2010 From: Greece, Thessaloniki Posts: 1,990 Thanks: 133 Math Focus: pre pre pre pre pre pre pre pre pre pre pre pre calculus Re: differential equation use substitution methode [color=#000000]What mathbalarka has done..... remember that , now for .[/color] June 3rd, 2012, 04:16 AM #7 Math Team   Joined: Mar 2012 From: India, West Bengal Posts: 3,871 Thanks: 86 Math Focus: Number Theory Re: differential equation use substitution methode y'=1-y/x x*y'=x-y x*y'+y=x x*y'+x'*y=x (xy)'=x d(xy)=x*dx integrating, xy+c1=x^2/2+c2 xy=x^2/2+C y=x/2+C/x June 3rd, 2012, 04:21 AM #8 Math Team   Joined: Mar 2012 From: India, West Bengal Posts: 3,871 Thanks: 86 Math Focus: Number Theory Re: differential equation use substitution methode If you want, I can tell you the solution of a,b are constants Note: sorry for writing answers of previous questions without using  June 3rd, 2012, 08:42 AM #9 Member   Joined: Apr 2012 Posts: 47 Thanks: 0 Re: differential equation use substitution methode thx problems solved. now got an other one problem. how do i found out C is just C not lnC? how can i recognize it after intergration? example: other one confused June 3rd, 2012, 10:02 AM   #10
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Re: differential equation use substitution methode

Quote:
 Originally Posted by zell^ thx problems solved. now got an other one problem. how do i found out C is just C not lnC? how can i recognize it after intergration? example: other one confused
Can you explain your question more simply? I cant understand According to my calculations,
The genarel solution of is: Tags differential, equation, methode, substitution Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post sydfremmer Differential Equations 6 February 12th, 2013 12:45 PM alexmath Differential Equations 2 November 21st, 2012 11:49 AM jrkcolorado Linear Algebra 1 September 22nd, 2012 12:37 PM zell^ Differential Equations 3 June 8th, 2012 02:42 PM germanaries Real Analysis 0 March 18th, 2008 12:28 PM

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