Find the Vertex Form f(x)=-2x^2-20x-51

$f (x) = - 2 x^{2} - 20 x - 51$

Step 1

Write $f (x) = - 2 x^{2} - 20 x - 51$ as an equation.

$y = - 2 x^{2} - 20 x - 51$

Step 2

Complete the square for $- 2 x^{2} - 20 x - 51$ .

Use the form $a x^{2} + b x + c$ , to find the values of $a$ , $b$ , and $c$ .

$a = - 2$

$b = - 20$

$c = - 51$

Consider the vertex form of a parabola.

$a {(x + d)}^{2} + e$

Find the value of $d$ using the formula $d = \frac{b}{2 a}$ .

Substitute the values of $a$ and $b$ into the formula $d = \frac{b}{2 a}$ .

$d = \frac{- 20}{2 \cdot - 2}$

Simplify the right side.

Cancel the common factor of $- 20$ and $2$ .

Factor $2$ out of $- 20$ .

$d = \frac{2 \cdot - 10}{2 \cdot - 2}$

Cancel the common factors.

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

$d = \frac{2 \cdot - 10}{2 (- 2)}$

Cancel the common factor.

$d = \frac{2 \cdot - 10}{2 \cdot - 2}$

Rewrite the expression.

$d = \frac{- 10}{- 2}$

Cancel the common factor of $- 10$ and $- 2$ .

Factor $- 2$ out of $- 10$ .

$d = \frac{- 2 (5)}{- 2}$

Cancel the common factors.

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

$d = \frac{- 2 \cdot 5}{- 2 \cdot 1}$

Cancel the common factor.

$d = \frac{- 2 \cdot 5}{- 2 \cdot 1}$

Rewrite the expression.

$d = \frac{5}{1}$

Divide $5$ by $1$ .

$d = 5$

Find the value of $e$ using the formula $e = c - \frac{b^{2}}{4 a}$ .

Substitute the values of $c$ , $b$ and $a$ into the formula $e = c - \frac{b^{2}}{4 a}$ .

$e = - 51 - \frac{{(- 20)}^{2}}{4 \cdot - 2}$

Simplify the right side.

Simplify each term.

Raise $- 20$ to the power of $2$ .

$e = - 51 - \frac{400}{4 \cdot - 2}$

Multiply $4$ by $- 2$ .

$e = - 51 - \frac{400}{- 8}$

Divide $400$ by $- 8$ .

$e = - 51 - - 50$

Multiply $- 1$ by $- 50$ .

$e = - 51 + 50$

Add $- 51$ and $50$ .

$e = - 1$

Substitute the values of $a$ , $d$ , and $e$ into the vertex form $- 2 {(x + 5)}^{2} - 1$ .

$- 2 {(x + 5)}^{2} - 1$

Step 3

Set $y$ equal to the new right side.

$y = - 2 {(x + 5)}^{2} - 1$

Find the Vertex Form f(x)=-2x^2-20x-51

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