Precalculus Examples

$f (x) = x^{2} + 5 x + 4$

Step 1

Rewrite the equation in vertex form.

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Step 1.1

Complete the square for $x^{2} + 5 x + 4$ .

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Step 1.1.1

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

$a = 1$

$b = 5$

$c = 4$

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

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Step 1.1.3.1

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

$d = \frac{5}{2 \cdot 1}$

Step 1.1.3.2

Multiply $2$ by $1$ .

$d = \frac{5}{2}$

Step 1.1.4

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

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Step 1.1.4.1

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

$e = 4 - \frac{5^{2}}{4 \cdot 1}$

Step 1.1.4.2

Simplify the right side.

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Step 1.1.4.2.1

Simplify each term.

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Step 1.1.4.2.1.1

Raise $5$ to the power of $2$ .

$e = 4 - \frac{25}{4 \cdot 1}$

Step 1.1.4.2.1.2

Multiply $4$ by $1$ .

$e = 4 - \frac{25}{4}$

Step 1.1.4.2.2

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

$e = 4 \cdot \frac{4}{4} - \frac{25}{4}$

Step 1.1.4.2.3

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

$e = \frac{4 \cdot 4}{4} - \frac{25}{4}$

Step 1.1.4.2.4

Combine the numerators over the common denominator.

$e = \frac{4 \cdot 4 - 25}{4}$

Step 1.1.4.2.5

Simplify the numerator.

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Step 1.1.4.2.5.1

Multiply $4$ by $4$ .

$e = \frac{16 - 25}{4}$

Step 1.1.4.2.5.2

Subtract $25$ from $16$ .

$e = \frac{- 9}{4}$

Step 1.1.4.2.6

Move the negative in front of the fraction.

$e = - \frac{9}{4}$

Step 1.1.5

Substitute the values of $a$ , $d$ , and $e$ into the vertex form ${(x + \frac{5}{2})}^{2} - \frac{9}{4}$ .

${(x + \frac{5}{2})}^{2} - \frac{9}{4}$

Step 1.2

Set $y$ equal to the new right side.

$y = {(x + \frac{5}{2})}^{2} - \frac{9}{4}$

Step 2

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

$a = 1$

$h = - \frac{5}{2}$

$k = - \frac{9}{4}$

Step 3

Find the vertex $(h, k)$ .

$(- \frac{5}{2}, - \frac{9}{4})$

Step 4