Find the Axis of Symmetry f(x)=2x^2-7x+4

$f (x) = 2 x^{2} - 7 x + 4$

Step 1

Write $f (x) = 2 x^{2} - 7 x + 4$ as an equation.

$y = 2 x^{2} - 7 x + 4$

Step 2

Rewrite the equation in vertex form.

Complete the square for $2 x^{2} - 7 x + 4$ .

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

$a = 2$

$b = - 7$

$c = 4$

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

$d = \frac{- 7}{2 \cdot 2}$

Simplify the right side.

Multiply $2$ by $2$ .

$d = \frac{- 7}{4}$

Move the negative in front of the fraction.

$d = - \frac{7}{4}$

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

$e = 4 - \frac{{(- 7)}^{2}}{4 \cdot 2}$

Simplify the right side.

Simplify each term.

Raise $- 7$ to the power of $2$ .

$e = 4 - \frac{49}{4 \cdot 2}$

Multiply $4$ by $2$ .

$e = 4 - \frac{49}{8}$

To write $4$ as a fraction with a common denominator, multiply by $\frac{8}{8}$ .

$e = 4 \cdot \frac{8}{8} - \frac{49}{8}$

Combine $4$ and $\frac{8}{8}$ .

$e = \frac{4 \cdot 8}{8} - \frac{49}{8}$

Combine the numerators over the common denominator.

$e = \frac{4 \cdot 8 - 49}{8}$

Simplify the numerator.

Multiply $4$ by $8$ .

$e = \frac{32 - 49}{8}$

Subtract $49$ from $32$ .

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

Move the negative in front of the fraction.

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

Substitute the values of $a$ , $d$ , and $e$ into the vertex form $2 {(x - \frac{7}{4})}^{2} - \frac{17}{8}$ .

$2 {(x - \frac{7}{4})}^{2} - \frac{17}{8}$

Set $y$ equal to the new right side.

$y = 2 {(x - \frac{7}{4})}^{2} - \frac{17}{8}$

Step 3

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

$a = 2$

$h = \frac{7}{4}$

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

Step 4

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

Opens Up

Step 5

Find the vertex $(h, k)$ .

$(\frac{7}{4}, - \frac{17}{8})$

Step 6

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 $2$ .

$\frac{1}{8}$

Step 7

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.

$(\frac{7}{4}, - 2)$

Step 8

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

$x = \frac{7}{4}$

Step 9

Find the Axis of Symmetry f(x)=2x^2-7x+4

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