
Calculus Calculus Math Forum 
 LinkBack  Thread Tools  Display Modes 
November 18th, 2012, 04:06 PM  #1 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Finding the Particular Solution of diff eqn
dy/dx = 8x^3 9x^2 + 4 and y =5, when x = 0 wanted to see this worked out in full ty 
November 18th, 2012, 04:10 PM  #2 
Senior Member Joined: Nov 2011 Posts: 595 Thanks: 16  Re: Finding the Particular Solution of diff eqn
Hi, Do you know what is the antiderivative of , , ...? 
November 18th, 2012, 04:25 PM  #3 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: Finding the Particular Solution of diff eqn
yes but am new to these x^3 = 3x^2 / 2 
November 18th, 2012, 04:52 PM  #4 
Senior Member Joined: Nov 2011 Posts: 595 Thanks: 16  Re: Finding the Particular Solution of diff eqn
New to these? Who are you kidding? It is like months you are asking for problems of that sort, actually this one is simpler than many you posted and that mostly Mark has guided you to the solution. Are you just copying any question that you have in your book to solve or are you trying to solve them before and then post? Learn to sweat a bit on your paper sheet, MarkFL will not always be by your side! (perhaps can we adopt a MarkFL? ) I don't want you to take it bad, I am just giving a honest advise, which is to try solving problem by yourself first (and then post if you are REALLY stuck)...and this one I am sure you could have solved if you had really wanted? No? For the answer you know the antiderivative of x^2 is x^3/3 (I am not using latex since you seem not to like it ) of x^3 is x^4/4...etc...(try to remember it for now... ) so y=(8/4)x^4(9/3)x^3+(4/1)x+cte so y=2x^43x^3+4x+cte. Since you want y(0)=5 this means, cte=5. cheers. PS: To do latex just write exactly what you usually do but press latex on the little box above. What's complicate about it? What about to celebrate your 700 posts you start doing this? 
November 18th, 2012, 05:05 PM  #5 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: Finding the Particular Solution of diff eqn
Thx Dougy 
November 18th, 2012, 05:17 PM  #6 
Senior Member Joined: Nov 2011 Posts: 595 Thanks: 16  Re: Finding the Particular Solution of diff eqn
Great! Sorry if I have been a bit harsh, I am glad you understood I am trying to go in a constructive way, not the opposite... it is very good that you are studying all these exercises at the end! Now think, could you solve another problem similar to this one? For instance could you do the equivalent problem and we want y to be equal to 5 at x=1, meaning y(1)=5? If you can do this, this means that you can do any problem like this with powers of x and when you see this in your exam that will be a peace of cake! 
November 18th, 2012, 06:35 PM  #7 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: Finding the Particular Solution of diff eqn
I think this is wrong. Maybe u can point out my errors 6x^6/6 + x^5/5 2x^3/3 + 4x^2/2 + Csub1 ? 
November 18th, 2012, 07:02 PM  #8 
Senior Member Joined: Nov 2011 Posts: 595 Thanks: 16  Re: Finding the Particular Solution of diff eqn
Almost good! (but the fact that you still don't want to use latex ) You did a mistake in the coefficient in , it should be Do you see it? All the rest looks good! What about the value of the constant? y(1)=5, so what is Csub1? Plug x=1 and y(1)=5 and you will obtain an equation and you can solve for Csub1 and obtain its value. For the Latex thing, so you write things like y=5x^5+3x^2 for instance, now you write the exact same thing but inside the latex...you press the little box "latex" (I guess you can find it ) and write inside, not that complicate right? For each equation you have to start a new latex box and in between you write as you do normally. You want a sin, write \sin, a cos write \cos, an integral write \int, you want to write x/3 write \frac{x}{3} so like [ latex]\frac{x}{3}[/latex]= or [ latex]x^3[/latex]= edit: Actually I did not pay enough attention, all coefficients are wrong! I don't have time now to explain but you still have not understood this...try to work more on it and find your mistakes. Even if you have the correct solution to the other problem you will do wrong at your quiz on such questions as long as you don't know how to do them YOURSELF. We can discuss this later, try to work on it..you are not that far to understand!! Courage! 
November 18th, 2012, 07:26 PM  #9 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: Finding the Particular Solution of diff eqn
ok I will review in my book at work the problem again from start to finish. Also, I am going to post a new problem This one is an approximation problem. I will show as much work as I can ps...I will post it with LATEX or at least try 
November 18th, 2012, 08:07 PM  #10 
Senior Member Joined: Aug 2012 From: South Carolina Posts: 866 Thanks: 0  Re: Finding the Particular Solution of diff eqn
Here we go ..from start to finish... = find particular solution when y = 5, when x =0 dx y = y = now when y = 5 and x = 0 C must equal 5 ? 

Tags 
diff, eqn, finding, solution 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Is this an ordinary diff eq or a partial diff eq?  Niko Bellic  Calculus  2  July 8th, 2013 10:01 AM 
need help finding solution ....  sokaris  Advanced Statistics  1  August 17th, 2009 11:48 AM 
Finding solution (X, Y, Z) that satisfies EQW  Mathmen  Abstract Algebra  1  May 18th, 2009 05:39 AM 
Finding diff equ  Daniiel  Calculus  0  September 13th, 2008 08:22 PM 
1st order nonlinear Diff Equations: Any known solution?  Polle  Applied Math  0  December 5th, 2007 09:38 AM 