Find the Maximum/Minimum Value g(x)=-2x^2-8x-9

$g (x) = - 2 x^{2} - 8 x - 9$

Step 1

The maximum of a quadratic function occurs at $x = - \frac{b}{2 a}$ . If $a$ is negative, the maximum value of the function is $f (- \frac{b}{2 a})$ .

$f_{max}$ $x = a x^{2} + b x + c$ occurs at $x = - \frac{b}{2 a}$

Step 2

Find the value of $x = - \frac{b}{2 a}$ .

Substitute in the values of $a$ and $b$ .

$x = - \frac{- 8}{2 (- 2)}$

Remove parentheses.

$x = - \frac{- 8}{2 (- 2)}$

Simplify $- \frac{- 8}{2 (- 2)}$ .

Cancel the common factor of $- 8$ and $2$ .

Factor $2$ out of $- 8$ .

$x = - \frac{2 \cdot - 4}{2 \cdot - 2}$

Cancel the common factors.

Factor $2$ out of $2 \cdot - 2$ .

$x = - \frac{2 \cdot - 4}{2 (- 2)}$

Cancel the common factor.

$x = - \frac{2 \cdot - 4}{2 \cdot - 2}$

Rewrite the expression.

$x = - \frac{- 4}{- 2}$

Cancel the common factor of $- 4$ and $- 2$ .

Factor $- 2$ out of $- 4$ .

$x = - \frac{- 2 (2)}{- 2}$

Cancel the common factors.

Factor $- 2$ out of $- 2$ .

$x = - \frac{- 2 \cdot 2}{- 2 \cdot 1}$

Cancel the common factor.

$x = - \frac{- 2 \cdot 2}{- 2 \cdot 1}$

Rewrite the expression.

$x = - \frac{2}{1}$

Divide $2$ by $1$ .

$x = - 1 \cdot 2$

Multiply $- 1$ by $2$ .

$x = - 2$

Step 3

Evaluate $f (- 2)$ .

Replace the variable $x$ with $- 2$ in the expression.

$g (- 2) = - 2 {(- 2)}^{2} - 8 \cdot - 2 - 9$

Simplify the result.

Simplify each term.

Multiply $- 2$ by ${(- 2)}^{2}$ by adding the exponents.

Multiply $- 2$ by ${(- 2)}^{2}$ .

Raise $- 2$ to the power of $1$ .

$g (- 2) = (- 2) {(- 2)}^{2} - 8 \cdot - 2 - 9$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$g (- 2) = {(- 2)}^{1 + 2} - 8 \cdot - 2 - 9$

Add $1$ and $2$ .

$g (- 2) = {(- 2)}^{3} - 8 \cdot - 2 - 9$

Raise $- 2$ to the power of $3$ .

$g (- 2) = - 8 - 8 \cdot - 2 - 9$

Multiply $- 8$ by $- 2$ .

$g (- 2) = - 8 + 16 - 9$

Simplify by adding and subtracting.

Add $- 8$ and $16$ .

$g (- 2) = 8 - 9$

Subtract $9$ from $8$ .

$g (- 2) = - 1$

The final answer is $- 1$ .

$- 1$

Step 4

Use the $x$ and $y$ values to find where the maximum occurs.

$(- 2, - 1)$

Step 5

Find the Maximum/Minimum Value g(x)=-2x^2-8x-9

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