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MORE MATH HELP. I hope someone can help me.

V

VTboy

Banned
I had a problem getting someone to help me the other day when I posted a math question, but I hope someone can do this one.

(y^(1/2))(dy/dx)+y^(3/2)=1

First I divide each term by y^(1/2) to get (dy/dx)+y=y^(-1/2)

next I say w=y^(3/2)

then dw/dx=3/2(y^(1/2))(dy/dx)

then I multiply both sides of (dy/dx)+y=y^(-1/2) by 3/2(y^(1/2)) to get

3/2[y^(1/2)](dy/dx)+3/2(y^(3/2))=3/2

So we plug dw/dx in and w to get

dw/dx+3/2w=3/2 since this is linear I say

u=e^(integral(3/2dx)) then you get u=e^(3x/2)

now I multiply each side of this dw/dx+3/2w=3/2 by e^(3x/2) to get

e^(3x/2)(dw/dx)+3/2w(e^(3x/2) )=3/2(e^(3x/2) )
I simplify this into d[(e^(3x/2))w]=3/2(e^(3x/2) )

take the integral of both sides to get [e^(3x/2)]w=e^(3x/2)+c
plug y^^(3/2) back into w and simply and the final anser is y^(3/2)=1+c[e^(-3x/2)]
 
This is for my DE class so I would greatly appreciate any help. Also this is a Bernoulli Equation if that jogs any memory.
 
Hmm, I made an easy A in Diffy Q, but the only thing I really remember is Laplace (which I use all the time), nowadays anytime I need a non-linear Diffy Q solved I use MatLab 😉.

But, I can't even tell what you are asking, so I have no idea how to help you. Are you just trying to see if your solution is correct? (Oh BTW: What book are you using?)
 
Well like I said in my above post I just wanted to solve the DE. You know get rid of the derivative. Our book is called a "A first course in Differential Equations the Classic 5th edition" it is just a reprint of the 5th edition.
 
BTW: A easy way to check diffy is just plug your solution back into the original problem. Like if you have y"+y'^6+y=12 then you find y, just plug it back in (of course you'll have to find y' and y" as well). This is real easy to do on Math software or a TI-89, good way to check (BTW: a great software package is Derive from TI real good for doing small stuff like this.) That being said, only use the software to check your solutions, as you'll never learn Diffy unless you use it a lot, by hand.
 
Originally posted by: VTboy
Well like I said in my above post I just wanted to solve the DE. You know get rid of the derivative. Our book is called a "A first course in Differential Equations the Classic 5th edition" it is just a reprint of the 5th edition.
Click to expand...

That is a great book. I took Diffy as a 8 week class, and I missed the first 2 weeks. Taught it all to myself out of that book in about 1.5 days.
 
Originally posted by: Zorba
Originally posted by: VTboy
Well like I said in my above post I just wanted to solve the DE. You know get rid of the derivative. Our book is called a "A first course in Differential Equations the Classic 5th edition" it is just a reprint of the 5th edition.
Click to expand...

That is a great book. I took Diffy as a 8 week class, and I missed the first 2 weeks. Taught it all to myself out of that book in about 1.5 days.
Click to expand...

Eight week class? That's bogus! Mine is 16 weeks.
 
Originally posted by: Dissipate
Originally posted by: Zorba
Originally posted by: VTboy
Well like I said in my above post I just wanted to solve the DE. You know get rid of the derivative. Our book is called a "A first course in Differential Equations the Classic 5th edition" it is just a reprint of the 5th edition.
Click to expand...

That is a great book. I took Diffy as a 8 week class, and I missed the first 2 weeks. Taught it all to myself out of that book in about 1.5 days.
Click to expand...

Eight week class? That's bogus! Mine is 16 weeks.
Click to expand...

Summer school has 8 week classes, as in you go to school 6 hours a week for 8 weeks instead of 3 hours a week for 16 weeks. If you do the math, total class time is equal.

its Diff EQ, not Diffy Q, wtf does Diffy Q mean?
Click to expand...

Actually it is Differential Equations, my friend. But if you like to shorten class names, as I do, you can call it whatever the hell you want. I first saw Diffy Q from my Engineering Physics one professor and I liked it better than Diff EQ, Diff E, Calc. 4 or Differential Equations, so that is what I use.
 
Originally posted by: Zorba
Originally posted by: Dissipate
Originally posted by: Zorba
Originally posted by: VTboy
Well like I said in my above post I just wanted to solve the DE. You know get rid of the derivative. Our book is called a "A first course in Differential Equations the Classic 5th edition" it is just a reprint of the 5th edition.
Click to expand...

That is a great book. I took Diffy as a 8 week class, and I missed the first 2 weeks. Taught it all to myself out of that book in about 1.5 days.
Click to expand...

Eight week class? That's bogus! Mine is 16 weeks.
Click to expand...

Summer school has 8 week classes, as in you go to school 6 hours a week for 8 weeks instead of 3 hours a week for 16 weeks. If you do the math, total class time is equal.

its Diff EQ, not Diffy Q, wtf does Diffy Q mean?
Click to expand...



Actually it is Differential Equations, my friend. But if you like to shorten class names, as I do, you can call it whatever the hell you want. I first saw Diffy Q from my Engineering Physics one professor and I liked it better than Diff EQ, Diff E, Calc. 4 or Differential Equations, so that is what I use.
Click to expand...

Calc 4? Calc 4 is Vector Calc, not Diff. Eq. in my neck of the woods.

 
its Diff EQ, not Diffy Q, wtf does Diffy Q mean?
Click to expand...

Actually it is Differential Equations, my friend. But if you like to shorten class names, as I do, you can call it whatever the hell you want. I first saw Diffy Q from my Engineering Physics one professor and I liked it better than Diff EQ, Diff E, Calc. 4 or Differential Equations, so that is what I use.
Click to expand...

actually, it's stfu, i know it's Differential Equations. But shortening it as Diffy Q doesn't make any sense. Diff Eq (Diff - Differential, EQ - Equations in case you didn't understand) is the correct way and the only correct way.
 
Originally posted by: HonkeyDonk
its Diff EQ, not Diffy Q, wtf does Diffy Q mean?
Click to expand...

Actually it is Differential Equations, my friend. But if you like to shorten class names, as I do, you can call it whatever the hell you want. I first saw Diffy Q from my Engineering Physics one professor and I liked it better than Diff EQ, Diff E, Calc. 4 or Differential Equations, so that is what I use.
Click to expand...

actually, it's stfu, i know it's Differential Equations. But shortening it as Diffy Q doesn't make any sense. Diff Eq (Diff - Differential, EQ - Equations in case you didn't understand) is the correct way and the only correct way.
Click to expand...

calm down man it's ok 😛
 
Originally posted by: HonkeyDonk
its Diff EQ, not Diffy Q, wtf does Diffy Q mean?
Click to expand...

Actually it is Differential Equations, my friend. But if you like to shorten class names, as I do, you can call it whatever the hell you want. I first saw Diffy Q from my Engineering Physics one professor and I liked it better than Diff EQ, Diff E, Calc. 4 or Differential Equations, so that is what I use.
Click to expand...

actually, it's stfu, i know it's Differential Equations. But shortening it as Diffy Q doesn't make any sense. Diff Eq (Diff - Differential, EQ - Equations in case you didn't understand) is the correct way and the only correct way.
Click to expand...

HAHAHAHHAHAHA thanks for making my day asshole
 
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