Graph y=2x^2-8x+6

$y = 2 x^{2} - 8 x + 6$

Step 1

Find the properties of the given parabola.

Rewrite the equation in vertex form.

Complete the square for $2 x^{2} - 8 x + 6$ .

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

$a = 2$

$b = - 8$

$c = 6$

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 $d = \frac{b}{2 a}$ .

$d = \frac{- 8}{2 \cdot 2}$

Simplify the right side.

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

Factor $2$ out of $- 8$ .

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

Cancel the common factors.

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

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

Cancel the common factor.

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

Rewrite the expression.

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

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

Factor $2$ out of $- 4$ .

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

Cancel the common factors.

Factor $2$ out of $2$ .

$d = \frac{2 \cdot - 2}{2 (1)}$

Cancel the common factor.

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

Rewrite the expression.

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

Divide $- 2$ by $1$ .

$d = - 2$

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 $e = c - \frac{b^{2}}{4 a}$ .

$e = 6 - \frac{{(- 8)}^{2}}{4 \cdot 2}$

Simplify the right side.

Simplify each term.

Raise $- 8$ to the power of $2$ .

$e = 6 - \frac{64}{4 \cdot 2}$

Multiply $4$ by $2$ .

$e = 6 - \frac{64}{8}$

Divide $64$ by $8$ .

$e = 6 - 1 \cdot 8$

Multiply $- 1$ by $8$ .

$e = 6 - 8$

Subtract $8$ from $6$ .

$e = - 2$

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

$2 {(x - 2)}^{2} - 2$

Set $y$ equal to the new right side.

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

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

$a = 2$

$h = 2$

$k = - 2$

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

Opens Up

Find the vertex $(h, k)$ .

$(2, - 2)$

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.

$(2, - \frac{15}{8})$

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.

$y = - \frac{17}{8}$

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

Direction: Opens Up

Vertex: $(2, - 2)$

Focus: $(2, - \frac{15}{8})$

Axis of Symmetry: $x = 2$

Directrix: $y = - \frac{17}{8}$

Direction: Opens Up

Vertex: $(2, - 2)$

Focus: $(2, - \frac{15}{8})$

Axis of Symmetry: $x = 2$

Directrix: $y = - \frac{17}{8}$

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 $1$ in the expression.

$f (1) = 2 {(1)}^{2} - 8 \cdot 1 + 6$

Simplify the result.

Simplify each term.

One to any power is one.

$f (1) = 2 \cdot 1 - 8 \cdot 1 + 6$

Multiply $2$ by $1$ .

$f (1) = 2 - 8 \cdot 1 + 6$

Multiply $- 8$ by $1$ .

$f (1) = 2 - 8 + 6$

Simplify by adding and subtracting.

Subtract $8$ from $2$ .

$f (1) = - 6 + 6$

Add $- 6$ and $6$ .

$f (1) = 0$

The final answer is $0$ .

$0$

The $y$ value at $x = 1$ is $0$ .

$y = 0$

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

$f (0) = 2 {(0)}^{2} - 8 \cdot 0 + 6$

Simplify the result.

Simplify each term.

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

$f (0) = 2 \cdot 0 - 8 \cdot 0 + 6$

Multiply $2$ by $0$ .

$f (0) = 0 - 8 \cdot 0 + 6$

Multiply $- 8$ by $0$ .

$f (0) = 0 + 0 + 6$

Simplify by adding numbers.

Add $0$ and $0$ .

$f (0) = 0 + 6$

Add $0$ and $6$ .

$f (0) = 6$

The final answer is $6$ .

$6$

The $y$ value at $x = 0$ is $6$ .

$y = 6$

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

$f (3) = 2 {(3)}^{2} - 8 \cdot 3 + 6$

Simplify the result.

Simplify each term.

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

$f (3) = 2 \cdot 9 - 8 \cdot 3 + 6$

Multiply $2$ by $9$ .

$f (3) = 18 - 8 \cdot 3 + 6$

Multiply $- 8$ by $3$ .

$f (3) = 18 - 24 + 6$

Simplify by adding and subtracting.

Subtract $24$ from $18$ .

$f (3) = - 6 + 6$

Add $- 6$ and $6$ .

$f (3) = 0$

The final answer is $0$ .

$0$

The $y$ value at $x = 3$ is $0$ .

$y = 0$

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

$f (4) = 2 {(4)}^{2} - 8 \cdot 4 + 6$

Simplify the result.

Simplify each term.

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

$f (4) = 2 \cdot 16 - 8 \cdot 4 + 6$

Multiply $2$ by $16$ .

$f (4) = 32 - 8 \cdot 4 + 6$

Multiply $- 8$ by $4$ .

$f (4) = 32 - 32 + 6$

Simplify by adding and subtracting.

Subtract $32$ from $32$ .

$f (4) = 0 + 6$

Add $0$ and $6$ .

$f (4) = 6$

The final answer is $6$ .

$6$

The $y$ value at $x = 4$ is $6$ .

$y = 6$

Graph the parabola using its properties and the selected points.

$\begin{array}{c} x & y \\ 0 & 6 \\ 1 & 0 \\ 2 & - 2 \\ 3 & 0 \\ 4 & 6 \end{array}$

Step 3

Graph the parabola using its properties and the selected points.

Direction: Opens Up

Vertex: $(2, - 2)$

Focus: $(2, - \frac{15}{8})$

Axis of Symmetry: $x = 2$

Directrix: $y = - \frac{17}{8}$

$\begin{array}{c} x & y \\ 0 & 6 \\ 1 & 0 \\ 2 & - 2 \\ 3 & 0 \\ 4 & 6 \end{array}$

Step 4

Graph y=2x^2-8x+6

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