Find Minimum Value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$

In summary, the purpose of finding the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$ is to determine the lowest possible value that the expression can have. To find the minimum value, techniques such as differentiation or completing the square can be used. The minimum value cannot be negative and there are restrictions on the values of x and y. Additionally, it is possible for the minimum value to be achieved at multiple points.
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anemone
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Find the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$ for $0<x<\sqrt{2}$ and $y>0$.
 
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anemone said:
Find the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$ for $0<x<\sqrt{2}$ and $y>0$.

Solution suggested by other:
The given function is the square of the distance between a point of the quarter of the circle $x^2+y^2=2$ in the open first quadrant and a point of the half hyperbola $xy=9$ in that quadrant. Then tangents to the curves at $(1,\,1)$ and $(3,\,3)$ separate the curves, and both are perpendicular to $x=y$, so those points are at the minimum distance, and the answer is $(3-1)^2+(1-3)^2=8$.
 

Related to Find Minimum Value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$

1. What is the purpose of finding the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$?

The purpose is to determine the lowest possible value that the expression can have, which can be useful in optimization problems or in finding the equilibrium point of a system.

2. How do you find the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$?

To find the minimum value, we can use techniques such as differentiation or completing the square and setting the derivative or completed expression equal to 0.

3. Can the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$ be negative?

No, the minimum value cannot be negative because it is the square of a real number, and squares are always non-negative.

4. Are there any restrictions on the values of x and y in $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$?

Yes, there are restrictions on the values of x and y. For the expression to be defined, x must be between -√2 and √2, and y must be non-zero.

5. Can the minimum value of $(x-y)^2+\left( \sqrt{2-x^2}-\dfrac{9}{y} \right)^2$ be achieved at multiple points?

Yes, it is possible for the minimum value to be achieved at multiple points, especially if the expression contains absolute values or has multiple local minimums.

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