Graph y=2(x-1)^2-4

$y = 2 {(x - 1)}^{2} - 4$

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 $k$ .

$a = 2$

$h = 1$

$k = - 4$

Since the value of $a$ is positive, the parabola opens up.

Opens Up

Find the vertex $(h, k)$ .

$(1, - 4)$

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.

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

Multiply $4$ by $2$ .

$\frac{1}{8}$

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.

$(1, - \frac{31}{8})$

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

$x = 1$

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.

$y = - \frac{33}{8}$

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

Direction: Opens Up

Vertex: $(1, - 4)$

Focus: $(1, - \frac{31}{8})$

Axis of Symmetry: $x = 1$

Directrix: $y = - \frac{33}{8}$

Direction: Opens Up

Vertex: $(1, - 4)$

Focus: $(1, - \frac{31}{8})$

Axis of Symmetry: $x = 1$

Directrix: $y = - \frac{33}{8}$

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 $0$ in the expression.

$f (0) = 2 {(0)}^{2} - 4 \cdot 0 - 2$

Simplify the result.

Simplify each term.

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

$f (0) = 2 \cdot 0 - 4 \cdot 0 - 2$

Multiply $2$ by $0$ .

$f (0) = 0 - 4 \cdot 0 - 2$

Multiply $- 4$ by $0$ .

$f (0) = 0 + 0 - 2$

Simplify by adding and subtracting.

Add $0$ and $0$ .

$f (0) = 0 - 2$

Subtract $2$ from $0$ .

$f (0) = - 2$

The final answer is $- 2$ .

$- 2$

The $y$ value at $x = 0$ is $- 2$ .

$y = - 2$

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

$f (- 1) = 2 {(- 1)}^{2} - 4 \cdot - 1 - 2$

Simplify the result.

Simplify each term.

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

$f (- 1) = 2 \cdot 1 - 4 \cdot - 1 - 2$

Multiply $2$ by $1$ .

$f (- 1) = 2 - 4 \cdot - 1 - 2$

Multiply $- 4$ by $- 1$ .

$f (- 1) = 2 + 4 - 2$

Simplify by adding and subtracting.

Add $2$ and $4$ .

$f (- 1) = 6 - 2$

Subtract $2$ from $6$ .

$f (- 1) = 4$

The final answer is $4$ .

$4$

The $y$ value at $x = - 1$ is $4$ .

$y = 4$

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

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

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 $1$ .

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

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

$f (2) = 2^{1 + 2} - 4 \cdot 2 - 2$

Add $1$ and $2$ .

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

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

$f (2) = 8 - 4 \cdot 2 - 2$

Multiply $- 4$ by $2$ .

$f (2) = 8 - 8 - 2$

Simplify by subtracting numbers.

Subtract $8$ from $8$ .

$f (2) = 0 - 2$

Subtract $2$ from $0$ .

$f (2) = - 2$

The final answer is $- 2$ .

$- 2$

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

$y = - 2$

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

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

Simplify the result.

Simplify each term.

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

$f (3) = 2 \cdot 9 - 4 \cdot 3 - 2$

Multiply $2$ by $9$ .

$f (3) = 18 - 4 \cdot 3 - 2$

Multiply $- 4$ by $3$ .

$f (3) = 18 - 12 - 2$

Simplify by subtracting numbers.

Subtract $12$ from $18$ .

$f (3) = 6 - 2$

Subtract $2$ from $6$ .

$f (3) = 4$

The final answer is $4$ .

$4$

The $y$ value at $x = 3$ is $4$ .

$y = 4$

Graph the parabola using its properties and the selected points.

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

Step 3

Graph the parabola using its properties and the selected points.

Direction: Opens Up

Vertex: $(1, - 4)$

Focus: $(1, - \frac{31}{8})$

Axis of Symmetry: $x = 1$

Directrix: $y = - \frac{33}{8}$

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

Step 4

Graph y=2(x-1)^2-4

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