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Change the independent variable to simplify the Euler equation, and then find a first integral of it.

4.∫x1x2yy'2+y2dx

Short Answer

Expert verified

Answer

The first integral of the Euler equation is x'=Cyy2-C2.

Step by step solution

01

Given Information

The given integral is∫x1x2yy'2+y2dx.

02

Definition of Euler equation    

For the integralI(ε)=F∫x1x2(x,y,y')dx, the Euler equation is mathematically presented as ddxdFdy'-dFdy=0.

03

Find the Euler equation of the given function


The given integral is ∫x1x2yy'2+y2dx.

First, let’s change the variables as follows:

∂F∂x'=x'y31+x'2y2∂F∂x=0

By using the two equations above, we can rewrite the integral.

∫yy2+y'2dx=∫yy2+y'2x'dy=∫yy2+x'-2x'dy=∫x'2y2+1dy

Let Fx,y,y'=yx'2y2+1.

By the definition of the Euler equation,ddy∂F∂x'-Ï€¹ó∂x=0.

Differentiate F with respect to x' and x.

∂F∂x'=x'y31+x'2y2∂F∂x=0

The Euler becomes as shown below.

ddxx'y31+x'2y2=0x'y31+x'2y2=C

The differential equation is x'=Cyy4-C2

Therefore, the first integral of the Euler equation is x'=Cyy4-C2

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