Graph f(x)=-3(x-2)^2-4

$f (x) = - 3 {(x - 2)}^{2} - 4$

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 $k$ .

$a = - 3$

$h = 2$

$k = - 4$

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

Opens Down

Find the vertex $(h, k)$ .

$(2, - 4)$

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.

$\frac{1}{4 \cdot - 3}$

Simplify.

Multiply $4$ by $- 3$ .

$\frac{1}{- 12}$

Move the negative in front of the fraction.

$- \frac{1}{12}$

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.

$(2, - \frac{49}{12})$

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

$x = 2$

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.

$y = - \frac{47}{12}$

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

Direction: Opens Down

Vertex: $(2, - 4)$

Focus: $(2, - \frac{49}{12})$

Axis of Symmetry: $x = 2$

Directrix: $y = - \frac{47}{12}$

Direction: Opens Down

Vertex: $(2, - 4)$

Focus: $(2, - \frac{49}{12})$

Axis of Symmetry: $x = 2$

Directrix: $y = - \frac{47}{12}$

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 $1$ in the expression.

$f (1) = - 3 {(1)}^{2} + 12 (1) - 16$

Simplify the result.

Simplify each term.

One to any power is one.

$f (1) = - 3 \cdot 1 + 12 (1) - 16$

Multiply $- 3$ by $1$ .

$f (1) = - 3 + 12 (1) - 16$

Multiply $12$ by $1$ .

$f (1) = - 3 + 12 - 16$

Simplify by adding and subtracting.

Add $- 3$ and $12$ .

$f (1) = 9 - 16$

Subtract $16$ from $9$ .

$f (1) = - 7$

The final answer is $- 7$ .

$- 7$

The $y$ value at $x = 1$ is $- 7$ .

$y = - 7$

Replace the variable $x$ with $0$ in the expression.

$f (0) = - 3 {(0)}^{2} + 12 (0) - 16$

Simplify the result.

Simplify each term.

Raising $0$ to any positive power yields $0$ .

$f (0) = - 3 \cdot 0 + 12 (0) - 16$

Multiply $- 3$ by $0$ .

$f (0) = 0 + 12 (0) - 16$

Multiply $12$ by $0$ .

$f (0) = 0 + 0 - 16$

Simplify by adding and subtracting.

Add $0$ and $0$ .

$f (0) = 0 - 16$

Subtract $16$ from $0$ .

$f (0) = - 16$

The final answer is $- 16$ .

$- 16$

The $y$ value at $x = 0$ is $- 16$ .

$y = - 16$

Replace the variable $x$ with $3$ in the expression.

$f (3) = - 3 {(3)}^{2} + 12 (3) - 16$

Simplify the result.

Simplify each term.

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

$f (3) = - 3 \cdot 9 + 12 (3) - 16$

Multiply $- 3$ by $9$ .

$f (3) = - 27 + 12 (3) - 16$

Multiply $12$ by $3$ .

$f (3) = - 27 + 36 - 16$

Simplify by adding and subtracting.

Add $- 27$ and $36$ .

$f (3) = 9 - 16$

Subtract $16$ from $9$ .

$f (3) = - 7$

The final answer is $- 7$ .

$- 7$

The $y$ value at $x = 3$ is $- 7$ .

$y = - 7$

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

$f (4) = - 3 {(4)}^{2} + 12 (4) - 16$

Simplify the result.

Simplify each term.

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

$f (4) = - 3 \cdot 16 + 12 (4) - 16$

Multiply $- 3$ by $16$ .

$f (4) = - 48 + 12 (4) - 16$

Multiply $12$ by $4$ .

$f (4) = - 48 + 48 - 16$

Simplify by adding and subtracting.

Add $- 48$ and $48$ .

$f (4) = 0 - 16$

Subtract $16$ from $0$ .

$f (4) = - 16$

The final answer is $- 16$ .

$- 16$

The $y$ value at $x = 4$ is $- 16$ .

$y = - 16$

Graph the parabola using its properties and the selected points.

$\begin{array}{c} x & y \\ 0 & - 16 \\ 1 & - 7 \\ 2 & - 4 \\ 3 & - 7 \\ 4 & - 16 \end{array}$

Step 3

Graph the parabola using its properties and the selected points.

Direction: Opens Down

Vertex: $(2, - 4)$

Focus: $(2, - \frac{49}{12})$

Axis of Symmetry: $x = 2$

Directrix: $y = - \frac{47}{12}$

$\begin{array}{c} x & y \\ 0 & - 16 \\ 1 & - 7 \\ 2 & - 4 \\ 3 & - 7 \\ 4 & - 16 \end{array}$

Step 4

Graph f(x)=-3(x-2)^2-4

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