Solve the non-linear DE $y' = xy+ y^{1/2}$ analytically [closed]
I've tried the Bernoulli Eq technique, $y=ux$ substitution technique, but nothing seemed to work out. Any ideas?
differential-equations
closed as off-topic by José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy Nov 30 at 15:04
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I've tried the Bernoulli Eq technique, $y=ux$ substitution technique, but nothing seemed to work out. Any ideas?
differential-equations
closed as off-topic by José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy Nov 30 at 15:04
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy
If this question can be reworded to fit the rules in the help center, please edit the question.
I take it that you think of $y'=xy+y^{1/2}$ otherwise the equation is linear.
– Martin
Nov 30 at 6:07
@Kenisha please check if the formatting corresponds to your DE.
– user376343
Nov 30 at 6:14
add a comment |
I've tried the Bernoulli Eq technique, $y=ux$ substitution technique, but nothing seemed to work out. Any ideas?
differential-equations
I've tried the Bernoulli Eq technique, $y=ux$ substitution technique, but nothing seemed to work out. Any ideas?
differential-equations
differential-equations
edited Nov 30 at 6:12
user376343
2,7782822
2,7782822
asked Nov 30 at 5:59
Kenisha Stills
111
111
closed as off-topic by José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy Nov 30 at 15:04
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy
If this question can be reworded to fit the rules in the help center, please edit the question.
closed as off-topic by José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy Nov 30 at 15:04
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "This question is missing context or other details: Please improve the question by providing additional context, which ideally includes your thoughts on the problem and any attempts you have made to solve it. This information helps others identify where you have difficulties and helps them write answers appropriate to your experience level." – José Carlos Santos, Henrik, Vidyanshu Mishra, Saad, amWhy
If this question can be reworded to fit the rules in the help center, please edit the question.
I take it that you think of $y'=xy+y^{1/2}$ otherwise the equation is linear.
– Martin
Nov 30 at 6:07
@Kenisha please check if the formatting corresponds to your DE.
– user376343
Nov 30 at 6:14
add a comment |
I take it that you think of $y'=xy+y^{1/2}$ otherwise the equation is linear.
– Martin
Nov 30 at 6:07
@Kenisha please check if the formatting corresponds to your DE.
– user376343
Nov 30 at 6:14
I take it that you think of $y'=xy+y^{1/2}$ otherwise the equation is linear.
– Martin
Nov 30 at 6:07
I take it that you think of $y'=xy+y^{1/2}$ otherwise the equation is linear.
– Martin
Nov 30 at 6:07
@Kenisha please check if the formatting corresponds to your DE.
– user376343
Nov 30 at 6:14
@Kenisha please check if the formatting corresponds to your DE.
– user376343
Nov 30 at 6:14
add a comment |
3 Answers
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Put $y=u^2$ so $y'=2uu'=xu^2+uRightarrow u'=frac 12xu+frac12$. Solve for $u$ using integrating factor and then find $y$.
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$y'=xy+y^{1/2} implies y'-xy=y^{1/2}$
So taking $p(x)=-x,q(x)=1, n={1/2}$
We have $y'+p(x)=q(x)y^n$
Applying Bernoulli's Equation
$$y^{1-n}=frac{(1-n)int e^{(1-n)int p(x)dx}q(x)dx+c_1}{e^{(1-n)int p(x)dx}}$$
Plugging in some terms we get
$$y^{1/2}=frac{(1/2)int e^{(-x^2/4)}dx+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=frac{(sqrt{pi}/2)operatorname{erf}(x/2)+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=e^{(x^2/4)}bigg((sqrt{pi}/2)operatorname{erf}(x/2)+c_1 bigg)$$
$$y=frac{pi}{4}e^{(x^2/2)}bigg(operatorname{erf}(x/2)+c_1 bigg)^2$$
Where $operatorname{erf}(z) =frac{2}{sqrt{pi}} int_0^z e^{-t^2} dt $ is the error function
add a comment |
As Guacho Perez answered, starting with $y=u^2$, you end with
$$u left(-2 u'+x u+1right)=0$$ Excluding the trivial case $u=0$, you then need to solve
$$2u'-xu=-1$$ Consider first
$$2u'-xu=0 implies frac{u'}u=frac x 2implies log(u)=frac {x^2} 4+Cimplies u=C e^{frac{x^2}{4}}$$ Now, use the integration factor or the variation of parameters to get
$$2 e^{frac{x^2}{4}} C'(x)=1implies C'=frac 12 e^{-frac{x^2}{4}}implies C=frac{sqrt{pi }}{2} text{erf}left(frac{x}{2}right)+K$$ then $u$ and $y$
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
add a comment |
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
Put $y=u^2$ so $y'=2uu'=xu^2+uRightarrow u'=frac 12xu+frac12$. Solve for $u$ using integrating factor and then find $y$.
add a comment |
Put $y=u^2$ so $y'=2uu'=xu^2+uRightarrow u'=frac 12xu+frac12$. Solve for $u$ using integrating factor and then find $y$.
add a comment |
Put $y=u^2$ so $y'=2uu'=xu^2+uRightarrow u'=frac 12xu+frac12$. Solve for $u$ using integrating factor and then find $y$.
Put $y=u^2$ so $y'=2uu'=xu^2+uRightarrow u'=frac 12xu+frac12$. Solve for $u$ using integrating factor and then find $y$.
answered Nov 30 at 6:27
Guacho Perez
3,88911131
3,88911131
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add a comment |
$y'=xy+y^{1/2} implies y'-xy=y^{1/2}$
So taking $p(x)=-x,q(x)=1, n={1/2}$
We have $y'+p(x)=q(x)y^n$
Applying Bernoulli's Equation
$$y^{1-n}=frac{(1-n)int e^{(1-n)int p(x)dx}q(x)dx+c_1}{e^{(1-n)int p(x)dx}}$$
Plugging in some terms we get
$$y^{1/2}=frac{(1/2)int e^{(-x^2/4)}dx+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=frac{(sqrt{pi}/2)operatorname{erf}(x/2)+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=e^{(x^2/4)}bigg((sqrt{pi}/2)operatorname{erf}(x/2)+c_1 bigg)$$
$$y=frac{pi}{4}e^{(x^2/2)}bigg(operatorname{erf}(x/2)+c_1 bigg)^2$$
Where $operatorname{erf}(z) =frac{2}{sqrt{pi}} int_0^z e^{-t^2} dt $ is the error function
add a comment |
$y'=xy+y^{1/2} implies y'-xy=y^{1/2}$
So taking $p(x)=-x,q(x)=1, n={1/2}$
We have $y'+p(x)=q(x)y^n$
Applying Bernoulli's Equation
$$y^{1-n}=frac{(1-n)int e^{(1-n)int p(x)dx}q(x)dx+c_1}{e^{(1-n)int p(x)dx}}$$
Plugging in some terms we get
$$y^{1/2}=frac{(1/2)int e^{(-x^2/4)}dx+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=frac{(sqrt{pi}/2)operatorname{erf}(x/2)+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=e^{(x^2/4)}bigg((sqrt{pi}/2)operatorname{erf}(x/2)+c_1 bigg)$$
$$y=frac{pi}{4}e^{(x^2/2)}bigg(operatorname{erf}(x/2)+c_1 bigg)^2$$
Where $operatorname{erf}(z) =frac{2}{sqrt{pi}} int_0^z e^{-t^2} dt $ is the error function
add a comment |
$y'=xy+y^{1/2} implies y'-xy=y^{1/2}$
So taking $p(x)=-x,q(x)=1, n={1/2}$
We have $y'+p(x)=q(x)y^n$
Applying Bernoulli's Equation
$$y^{1-n}=frac{(1-n)int e^{(1-n)int p(x)dx}q(x)dx+c_1}{e^{(1-n)int p(x)dx}}$$
Plugging in some terms we get
$$y^{1/2}=frac{(1/2)int e^{(-x^2/4)}dx+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=frac{(sqrt{pi}/2)operatorname{erf}(x/2)+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=e^{(x^2/4)}bigg((sqrt{pi}/2)operatorname{erf}(x/2)+c_1 bigg)$$
$$y=frac{pi}{4}e^{(x^2/2)}bigg(operatorname{erf}(x/2)+c_1 bigg)^2$$
Where $operatorname{erf}(z) =frac{2}{sqrt{pi}} int_0^z e^{-t^2} dt $ is the error function
$y'=xy+y^{1/2} implies y'-xy=y^{1/2}$
So taking $p(x)=-x,q(x)=1, n={1/2}$
We have $y'+p(x)=q(x)y^n$
Applying Bernoulli's Equation
$$y^{1-n}=frac{(1-n)int e^{(1-n)int p(x)dx}q(x)dx+c_1}{e^{(1-n)int p(x)dx}}$$
Plugging in some terms we get
$$y^{1/2}=frac{(1/2)int e^{(-x^2/4)}dx+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=frac{(sqrt{pi}/2)operatorname{erf}(x/2)+c_1}{e^{(-x^2/4)}}$$
$$y^{1/2}=e^{(x^2/4)}bigg((sqrt{pi}/2)operatorname{erf}(x/2)+c_1 bigg)$$
$$y=frac{pi}{4}e^{(x^2/2)}bigg(operatorname{erf}(x/2)+c_1 bigg)^2$$
Where $operatorname{erf}(z) =frac{2}{sqrt{pi}} int_0^z e^{-t^2} dt $ is the error function
answered Nov 30 at 6:41
Mason
1,9341530
1,9341530
add a comment |
add a comment |
As Guacho Perez answered, starting with $y=u^2$, you end with
$$u left(-2 u'+x u+1right)=0$$ Excluding the trivial case $u=0$, you then need to solve
$$2u'-xu=-1$$ Consider first
$$2u'-xu=0 implies frac{u'}u=frac x 2implies log(u)=frac {x^2} 4+Cimplies u=C e^{frac{x^2}{4}}$$ Now, use the integration factor or the variation of parameters to get
$$2 e^{frac{x^2}{4}} C'(x)=1implies C'=frac 12 e^{-frac{x^2}{4}}implies C=frac{sqrt{pi }}{2} text{erf}left(frac{x}{2}right)+K$$ then $u$ and $y$
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
add a comment |
As Guacho Perez answered, starting with $y=u^2$, you end with
$$u left(-2 u'+x u+1right)=0$$ Excluding the trivial case $u=0$, you then need to solve
$$2u'-xu=-1$$ Consider first
$$2u'-xu=0 implies frac{u'}u=frac x 2implies log(u)=frac {x^2} 4+Cimplies u=C e^{frac{x^2}{4}}$$ Now, use the integration factor or the variation of parameters to get
$$2 e^{frac{x^2}{4}} C'(x)=1implies C'=frac 12 e^{-frac{x^2}{4}}implies C=frac{sqrt{pi }}{2} text{erf}left(frac{x}{2}right)+K$$ then $u$ and $y$
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
add a comment |
As Guacho Perez answered, starting with $y=u^2$, you end with
$$u left(-2 u'+x u+1right)=0$$ Excluding the trivial case $u=0$, you then need to solve
$$2u'-xu=-1$$ Consider first
$$2u'-xu=0 implies frac{u'}u=frac x 2implies log(u)=frac {x^2} 4+Cimplies u=C e^{frac{x^2}{4}}$$ Now, use the integration factor or the variation of parameters to get
$$2 e^{frac{x^2}{4}} C'(x)=1implies C'=frac 12 e^{-frac{x^2}{4}}implies C=frac{sqrt{pi }}{2} text{erf}left(frac{x}{2}right)+K$$ then $u$ and $y$
As Guacho Perez answered, starting with $y=u^2$, you end with
$$u left(-2 u'+x u+1right)=0$$ Excluding the trivial case $u=0$, you then need to solve
$$2u'-xu=-1$$ Consider first
$$2u'-xu=0 implies frac{u'}u=frac x 2implies log(u)=frac {x^2} 4+Cimplies u=C e^{frac{x^2}{4}}$$ Now, use the integration factor or the variation of parameters to get
$$2 e^{frac{x^2}{4}} C'(x)=1implies C'=frac 12 e^{-frac{x^2}{4}}implies C=frac{sqrt{pi }}{2} text{erf}left(frac{x}{2}right)+K$$ then $u$ and $y$
answered Nov 30 at 6:50
Claude Leibovici
119k1157132
119k1157132
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
add a comment |
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
I'm probably not at as great as a school as you've all attended. I'm in Ohio. I haven't been taught error functions nor was aware of them.
– Kenisha Stills
Nov 30 at 12:36
add a comment |
I take it that you think of $y'=xy+y^{1/2}$ otherwise the equation is linear.
– Martin
Nov 30 at 6:07
@Kenisha please check if the formatting corresponds to your DE.
– user376343
Nov 30 at 6:14