The function is .

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As tends to ,  tends to .

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The function is .

Apply derivative on each side with respect to .

The function has extreme value.

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Substitute   and in .

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The function has minimum value at .

Graph:

Graph of is:

Observe the figure:

As the value of increases , the function is decreasing and minimum point is moving down.

The function has minimum value at .

As the value of increases , the function is decreasing and minimum point is moving down.