Find the Axis of Symmetry f(x)=-6x^2+24x-20

$f (x) = - 6 x^{2} + 24 x - 20$

Step 1

Write $f (x) = - 6 x^{2} + 24 x - 20$ as an equation.

$y = - 6 x^{2} + 24 x - 20$

Step 2

Rewrite the equation in vertex form.

Complete the square for $- 6 x^{2} + 24 x - 20$ .

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

$a = - 6$

$b = 24$

$c = - 20$

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

$d = \frac{24}{2 \cdot - 6}$

Simplify the right side.

Cancel the common factor of $24$ and $2$ .

Factor $2$ out of $24$ .

$d = \frac{2 \cdot 12}{2 \cdot - 6}$

Cancel the common factors.

Factor $2$ out of $2 \cdot - 6$ .

$d = \frac{2 \cdot 12}{2 (- 6)}$

Cancel the common factor.

$d = \frac{2 \cdot 12}{2 \cdot - 6}$

Rewrite the expression.

$d = \frac{12}{- 6}$

Cancel the common factor of $12$ and $- 6$ .

Factor $6$ out of $12$ .

$d = \frac{6 (2)}{- 6}$

Move the negative one from the denominator of $\frac{2}{- 1}$ .

$d = - 1 \cdot 2$

Multiply $- 1$ by $2$ .

$d = - 2$

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

$e = - 20 - \frac{24^{2}}{4 \cdot - 6}$

Simplify the right side.

Simplify each term.

Raise $24$ to the power of $2$ .

$e = - 20 - \frac{576}{4 \cdot - 6}$

Multiply $4$ by $- 6$ .

$e = - 20 - \frac{576}{- 24}$

Divide $576$ by $- 24$ .

$e = - 20 - - 24$

Multiply $- 1$ by $- 24$ .

$e = - 20 + 24$

Add $- 20$ and $24$ .

$e = 4$

Substitute the values of $a$ , $d$ , and $e$ into the vertex form $- 6 {(x - 2)}^{2} + 4$ .

$- 6 {(x - 2)}^{2} + 4$

Set $y$ equal to the new right side.

$y = - 6 {(x - 2)}^{2} + 4$

Step 3

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

$a = - 6$

$h = 2$

$k = 4$

Step 4

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

Opens Down

Step 5

Find the vertex $(h, k)$ .

$(2, 4)$

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.

$\frac{1}{4 \cdot - 6}$

Simplify.

Multiply $4$ by $- 6$ .

$\frac{1}{- 24}$

Move the negative in front of the fraction.

$- \frac{1}{24}$

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.

$(2, \frac{95}{24})$

Step 8

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

$x = 2$

Step 9

Find the Axis of Symmetry f(x)=-6x^2+24x-20

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