$\"\"$

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Critical number :

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A critical number of a function $\"\"$ is a number $\"\"$ in the domain of $\"\"$ such that either $\"\"$ or $\"\"$ does not exist.

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$\"\"$

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The function is $\"\"$ .

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$\"\"$ is differentiable at all values of $\"\"$ because it is a polynomial.

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Therefore, solutions of $\"\"$ are the critical numbers.

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Differentiate $\"\"$ on each side with respect to $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$ .

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Equate $\"\"$ to zero.

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$\"\"$

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$\"\"$ and $\"\"$

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Find the solutions of the quadratic equation $\"\"$ .

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$\"\"$

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The solutions of $\"\"$ are imaginary numbers, they are not considered.

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The critical number is $\"\"$ .

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The critical number is $\"\"$ .