There is an example in my textbook which I´m having trouble with.(adsbygoogle = window.adsbygoogle || []).push({});

The example is like this.

"

Find the area of the finite plane region bounded by the four parabolas, y=x^2 , y=2x^2 , x=y^2 , and x=3y^2

The region is called D.

Let u=y/x^2 and v=x/y^2

The the region D corresponds to the rectangle R in the uv - plane given by

1≤ u ≤2 and 1≤ v ≤3

"

The rest with the Jacobian determinant and so on I understand.

What I don't understand in this example is the expression

u=y/x^2 and v=x/y^2

I don't see why u and v are chosen this way.

It would be great if someone could explain this to me.

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# Homework Help: Change of variables in double integrals textbook problem

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