Graph y=-2(x+3)^2

$y = - 2 {(x + 3)}^{2}$

Step 1

Find the properties of the given parabola.

Use the vertex form, $y = a {(x - h)}^{2} + k$ , to determine the values of $a$ , $h$ , and $k$ .

$a = - 2$

$h = - 3$

$k = 0$

Since the value of $a$ is negative, the parabola opens down.

Opens Down

Find the vertex $(h, k)$ .

$(- 3, 0)$

Find $p$ , the distance from the vertex to the focus.

Find the distance from the vertex to a focus of the parabola by using the following formula.

$\frac{1}{4 a}$

Substitute the value of $a$ into the formula.

$\frac{1}{4 \cdot - 2}$

Simplify.

Multiply $4$ by $- 2$ .

$\frac{1}{- 8}$

Move the negative in front of the fraction.

$- \frac{1}{8}$

Find the focus.

The focus of a parabola can be found by adding $p$ to the y-coordinate $k$ if the parabola opens up or down.

$(h, k + p)$

Substitute the known values of $h$ , $p$ , and $k$ into the formula and simplify.

$(- 3, - \frac{1}{8})$

Find the axis of symmetry by finding the line that passes through the vertex and the focus.

$x = - 3$

Find the directrix.

The directrix of a parabola is the horizontal line found by subtracting $p$ from the y-coordinate $k$ of the vertex if the parabola opens up or down.

$y = k - p$

Substitute the known values of $p$ and $k$ into the formula and simplify.

$y = \frac{1}{8}$

Use the properties of the parabola to analyze and graph the parabola.

Direction: Opens Down

Vertex: $(- 3, 0)$

Focus: $(- 3, - \frac{1}{8})$

Axis of Symmetry: $x = - 3$

Directrix: $y = \frac{1}{8}$

Direction: Opens Down

Vertex: $(- 3, 0)$

Focus: $(- 3, - \frac{1}{8})$

Axis of Symmetry: $x = - 3$

Directrix: $y = \frac{1}{8}$

Step 2

Select a few $x$ values, and plug them into the equation to find the corresponding $y$ values. The $x$ values should be selected around the vertex.

Replace the variable $x$ with $- 4$ in the expression.

$f (- 4) = - 2 {(- 4)}^{2} - 12 \cdot - 4 - 18$

Simplify the result.

Simplify each term.

Raise $- 4$ to the power of $2$ .

$f (- 4) = - 2 \cdot 16 - 12 \cdot - 4 - 18$

Multiply $- 2$ by $16$ .

$f (- 4) = - 32 - 12 \cdot - 4 - 18$

Multiply $- 12$ by $- 4$ .

$f (- 4) = - 32 + 48 - 18$

Simplify by adding and subtracting.

Add $- 32$ and $48$ .

$f (- 4) = 16 - 18$

Subtract $18$ from $16$ .

$f (- 4) = - 2$

The final answer is $- 2$ .

$- 2$

The $y$ value at $x = - 4$ is $- 2$ .

$y = - 2$

Replace the variable $x$ with $- 5$ in the expression.

$f (- 5) = - 2 {(- 5)}^{2} - 12 \cdot - 5 - 18$

Simplify the result.

Simplify each term.

Raise $- 5$ to the power of $2$ .

$f (- 5) = - 2 \cdot 25 - 12 \cdot - 5 - 18$

Multiply $- 2$ by $25$ .

$f (- 5) = - 50 - 12 \cdot - 5 - 18$

Multiply $- 12$ by $- 5$ .

$f (- 5) = - 50 + 60 - 18$

Simplify by adding and subtracting.

Add $- 50$ and $60$ .

$f (- 5) = 10 - 18$

Subtract $18$ from $10$ .

$f (- 5) = - 8$

The final answer is $- 8$ .

$- 8$

The $y$ value at $x = - 5$ is $- 8$ .

$y = - 8$

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

$f (- 2) = - 2 {(- 2)}^{2} - 12 \cdot - 2 - 18$

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 $1$ .

$f (- 2) = (- 2) {(- 2)}^{2} - 12 \cdot - 2 - 18$

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

$f (- 2) = {(- 2)}^{1 + 2} - 12 \cdot - 2 - 18$

Add $1$ and $2$ .

$f (- 2) = {(- 2)}^{3} - 12 \cdot - 2 - 18$

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

$f (- 2) = - 8 - 12 \cdot - 2 - 18$

Multiply $- 12$ by $- 2$ .

$f (- 2) = - 8 + 24 - 18$

Simplify by adding and subtracting.

Add $- 8$ and $24$ .

$f (- 2) = 16 - 18$

Subtract $18$ from $16$ .

$f (- 2) = - 2$

The final answer is $- 2$ .

$- 2$

The $y$ value at $x = - 2$ is $- 2$ .

$y = - 2$

Replace the variable $x$ with $- 1$ in the expression.

$f (- 1) = - 2 {(- 1)}^{2} - 12 \cdot - 1 - 18$

Simplify the result.

Simplify each term.

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

$f (- 1) = - 2 \cdot 1 - 12 \cdot - 1 - 18$

Multiply $- 2$ by $1$ .

$f (- 1) = - 2 - 12 \cdot - 1 - 18$

Multiply $- 12$ by $- 1$ .

$f (- 1) = - 2 + 12 - 18$

Simplify by adding and subtracting.

Add $- 2$ and $12$ .

$f (- 1) = 10 - 18$

Subtract $18$ from $10$ .

$f (- 1) = - 8$

The final answer is $- 8$ .

$- 8$

The $y$ value at $x = - 1$ is $- 8$ .

$y = - 8$

Graph the parabola using its properties and the selected points.

$\begin{array}{c} x & y \\ - 5 & - 8 \\ - 4 & - 2 \\ - 3 & 0 \\ - 2 & - 2 \\ - 1 & - 8 \end{array}$

Step 3

Graph the parabola using its properties and the selected points.

Direction: Opens Down

Vertex: $(- 3, 0)$

Focus: $(- 3, - \frac{1}{8})$

Axis of Symmetry: $x = - 3$

Directrix: $y = \frac{1}{8}$

$\begin{array}{c} x & y \\ - 5 & - 8 \\ - 4 & - 2 \\ - 3 & 0 \\ - 2 & - 2 \\ - 1 & - 8 \end{array}$

Step 4

Graph y=-2(x+3)^2

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