Precalculus Examples

$f (x) = x^{2} - 2 x - 15$

Step 1

Rewrite the equation in vertex form.

Tap for more steps...

Step 1.1

Complete the square for $x^{2} - 2 x - 15$ .

Tap for more steps...

Step 1.1.1

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

$a = 1$

$b = - 2$

$c = - 15$

Step 1.1.2

Consider the vertex form of a parabola.

$a {(x + d)}^{2} + e$

Step 1.1.3

Find the value of $d$ using the formula $d = \frac{b}{2 a}$ .

Tap for more steps...

Step 1.1.3.1

Substitute the values of $a$ and $b$ into the formula $d = \frac{b}{2 a}$ .

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

Step 1.1.3.2

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

Tap for more steps...

Step 1.1.3.2.1

Factor $2$ out of $- 2$ .

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

Step 1.1.3.2.2

Cancel the common factors.

Tap for more steps...

Step 1.1.3.2.2.1

Factor $2$ out of $2 \cdot 1$ .

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

Step 1.1.3.2.2.2

Cancel the common factor.

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

Step 1.1.3.2.2.3

Rewrite the expression.

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

Step 1.1.3.2.2.4

Divide $- 1$ by $1$ .

$d = - 1$

Step 1.1.4

Find the value of $e$ using the formula $e = c - \frac{b^{2}}{4 a}$ .

Tap for more steps...

Step 1.1.4.1

Substitute the values of $c$ , $b$ and $a$ into the formula $e = c - \frac{b^{2}}{4 a}$ .

$e = - 15 - \frac{{(- 2)}^{2}}{4 \cdot 1}$

Step 1.1.4.2

Simplify the right side.

Tap for more steps...

Step 1.1.4.2.1

Simplify each term.

Tap for more steps...

Step 1.1.4.2.1.1

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

$e = - 15 - \frac{4}{4 \cdot 1}$

Step 1.1.4.2.1.2

Multiply $4$ by $1$ .

$e = - 15 - \frac{4}{4}$

Step 1.1.4.2.1.3

Cancel the common factor of $4$ .

Tap for more steps...

Step 1.1.4.2.1.3.1

Cancel the common factor.

$e = - 15 - \frac{4}{4}$

Step 1.1.4.2.1.3.2

Rewrite the expression.

$e = - 15 - 1 \cdot 1$

Step 1.1.4.2.1.4

Multiply $- 1$ by $1$ .

$e = - 15 - 1$

Step 1.1.4.2.2

Subtract $1$ from $- 15$ .

$e = - 16$

Step 1.1.5

Substitute the values of $a$ , $d$ , and $e$ into the vertex form ${(x - 1)}^{2} - 16$ .

${(x - 1)}^{2} - 16$

Step 1.2

Set $y$ equal to the new right side.

$y = {(x - 1)}^{2} - 16$

Step 2

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

$a = 1$

$h = 1$

$k = - 16$

Step 3

Find the vertex $(h, k)$ .

$(1, - 16)$

Step 4