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Is there a solution to the following differential equation: $$ \frac{dy}{dx}=2x-y^{2} $$ It is also given that:

y(0)= 1

I have tried to solve it using the integrating factor method, but that did not work nor did any transformations to try to make the equation linear. I also tried working with this equation as a Bernoulli equation, which did not work also I also tried substitutions to make this a Riccati equation, but it also did not work out

The substitution I tried to reduce to a linear equation were $$ y=-\frac{u'}{u} $$ The substitutions (rather guesses) I tried to reduce the equation to a Riccati type $$ y=-x $$ $$ y=x $$ None of them worked out I also tried working with this equation as a Bernouli type where I subbed: $$ \frac{1}{u}=y $$ where then: $$ \frac{dy}{dx}= -\frac{1}{u^{2}}\frac{du}{dx} $$ And later after I subbed it into the original equation and I simplified a bit I got: $$ \frac{du}{dx}=1-2xu^{2} $$ And I dont know where to procede from here

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  • $\begingroup$ Welcome to MSE. Your question is phrased as an isolated problem, without any further information or context. This does not match many users' quality standards, so it may attract downvotes, or be closed. To prevent that, please edit the question. This will help you recognize and resolve the issues. Concretely: please provide context, and include your work and thoughts on the problem. These changes can help in formulating more appropriate answers. $\endgroup$ Commented Apr 16 at 17:09
  • $\begingroup$ This is what W|A gives as a solution. Is there any reason you think this should have a nice solution? $\endgroup$ Commented Apr 16 at 17:13
  • $\begingroup$ @CameronL.Williams: Any idea what the specific solution associated with $y(0) =1$ is? $\endgroup$ Commented Apr 16 at 17:21
  • $\begingroup$ This differential equation was given as a question in a textbook, which is the reason why I hope it has a solution, and also, no additional information was given about particular solutions associated with y(0) =1 (also god knows why the textbook didnt give a solutions in the section of answers) $\endgroup$ Commented Apr 16 at 17:29
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    $\begingroup$ Use the substitution $y=+\frac{u'}{u}$. This will transform the ODE into an Airy differential equation. $\endgroup$ Commented Apr 16 at 17:31

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This ode is called reduced Riccati. It has direct solution because of this. i.e. its solution can be written directly without the need to solve associated Airy ode. (you can ofcourse still do that, but why?).

For the general Riccati, there is no such direct solution. Need to solve the associated second order Airy ode directly.

The reduced Riccati has the form

$$ y' = a x^n + b y^2 $$ There are 2 subcases. When $n=-2$ and when it is not.

Comparing the given ode to the above shows that \begin{align*} a &= 2\\ b &= -1\\ n &= 1 \end{align*} Since $n\neq -2$ then the solution of the reduced Riccati ode is given by (reference 1,reference 2, reference 3) \begin{align*} w & =\sqrt{x}\left\{ \begin{array}[c]{cc} c_{1}\operatorname{BesselJ}\left( \frac{1}{2k},\frac{1}{k}\sqrt{ab} x^{k}\right) +c_{2}\operatorname{BesselY}\left( \frac{1}{2k},\frac{1}% {k}\sqrt{ab}x^{k}\right) & ab>0\\ c_{1}\operatorname{BesselI}\left( \frac{1}{2k},\frac{1}{k}\sqrt{-ab}% x^{k}\right) +c_{2}\operatorname{BesselK}\left( \frac{1}{2k},\frac{1}% {k}\sqrt{-ab}x^{k}\right) & ab<0 \end{array} \right. \tag{1}\\ y & =-\frac{1}{b}\frac{w^{\prime}}{w}\nonumber\\ k &=1+\frac{n}{2}\nonumber \end{align*} Since $ab<0$ then EQ(1) gives \begin{align*} k &= {\frac{3}{2}}\\ w &= \sqrt{x}\, \left(c_1 \operatorname{BesselI}\left(\frac{1}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)+c_2 \operatorname{BesselK}\left(\frac{1}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)\right) \end{align*} Therefore the solution becomes \begin{align*} y & =-\frac{1}{b}\frac{w^{\prime}}{w} \end{align*} Substituting the value of $b,w$ found above and simplifying gives \begin{align*} y &= \frac{\sqrt{2}\, \sqrt{x}\, \left(\operatorname{BesselI}\left(-\frac{2}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right) c_1 -\operatorname{BesselK}\left(\frac{2}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right) c_2 \right)}{c_1 \operatorname{BesselI}\left(\frac{1}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)+c_2 \operatorname{BesselK}\left(\frac{1}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)} \end{align*} Letting $c_2 = 1$ the above becomes \begin{align*} y = \frac{\sqrt{2}\, \sqrt{x}\, \left(\operatorname{BesselI}\left(-\frac{2}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right) c_1 -\operatorname{BesselK}\left(\frac{2}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)\right)}{c_1 \operatorname{BesselI}\left(\frac{1}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)+\operatorname{BesselK}\left(\frac{1}{3}, \frac{2 \sqrt{2}\, x^{{3}/{2}}}{3}\right)} \end{align*}

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