Pre-Algebra Examples

$y = \frac{1}{4} \cdot ((x + 7) (x + 1))$

Step 1

Solve for $y$ .

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Step 1.1

Remove parentheses.

$y = \frac{1}{4} \cdot ((x + 7) (x + 1))$

Step 1.2

Simplify $\frac{1}{4} \cdot ((x + 7) (x + 1))$ .

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Step 1.2.1

Expand $(x + 7) (x + 1)$ using the FOIL Method.

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Step 1.2.1.1

Apply the distributive property.

$y = \frac{1}{4} \cdot (x (x + 1) + 7 (x + 1))$

Step 1.2.1.2

Apply the distributive property.

$y = \frac{1}{4} \cdot (x \cdot x + x \cdot 1 + 7 (x + 1))$

Step 1.2.1.3

Apply the distributive property.

$y = \frac{1}{4} \cdot (x \cdot x + x \cdot 1 + 7 x + 7 \cdot 1)$

Step 1.2.2

Simplify and combine like terms.

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Step 1.2.2.1

Simplify each term.

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Step 1.2.2.1.1

Multiply $x$ by $x$ .

$y = \frac{1}{4} \cdot (x^{2} + x \cdot 1 + 7 x + 7 \cdot 1)$

Step 1.2.2.1.2

Multiply $x$ by $1$ .

$y = \frac{1}{4} \cdot (x^{2} + x + 7 x + 7 \cdot 1)$

Step 1.2.2.1.3

Multiply $7$ by $1$ .

$y = \frac{1}{4} \cdot (x^{2} + x + 7 x + 7)$

Step 1.2.2.2

Add $x$ and $7 x$ .

$y = \frac{1}{4} \cdot (x^{2} + 8 x + 7)$

Step 1.2.3

Apply the distributive property.

$y = \frac{1}{4} x^{2} + \frac{1}{4} (8 x) + \frac{1}{4} \cdot 7$

Step 1.2.4

Simplify.

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Step 1.2.4.1

Combine $\frac{1}{4}$ and $x^{2}$ .

$y = \frac{x^{2}}{4} + \frac{1}{4} (8 x) + \frac{1}{4} \cdot 7$

Step 1.2.4.2

Cancel the common factor of $4$ .

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Step 1.2.4.2.1

Factor $4$ out of $8 x$ .

$y = \frac{x^{2}}{4} + \frac{1}{4} (4 (2 x)) + \frac{1}{4} \cdot 7$

Step 1.2.4.2.2

Cancel the common factor.

$y = \frac{x^{2}}{4} + \frac{1}{4} (4 (2 x)) + \frac{1}{4} \cdot 7$

Step 1.2.4.2.3

Rewrite the expression.

$y = \frac{x^{2}}{4} + 2 x + \frac{1}{4} \cdot 7$

Step 1.2.4.3

Combine $\frac{1}{4}$ and $7$ .

$y = \frac{x^{2}}{4} + 2 x + \frac{7}{4}$

Step 2

Find the properties of the given parabola.

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Step 2.1

Rewrite the equation in vertex form.

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Step 2.1.1

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

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Step 2.1.1.1

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

$a = \frac{1}{4}$

$b = 2$

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

Step 2.1.1.2

Consider the vertex form of a parabola.

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

Step 2.1.1.3

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

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Step 2.1.1.3.1

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

$d = \frac{2}{2 (\frac{1}{4})}$

Step 2.1.1.3.2

Simplify the right side.

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Step 2.1.1.3.2.1

Cancel the common factor of $2$ .

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Step 2.1.1.3.2.1.1

Cancel the common factor.

$d = \frac{2}{2 (\frac{1}{4})}$

Step 2.1.1.3.2.1.2

Rewrite the expression.

$d = \frac{1}{\frac{1}{4}}$

Step 2.1.1.3.2.2

Multiply the numerator by the reciprocal of the denominator.

$d = 1 \cdot 4$

Step 2.1.1.3.2.3

Multiply $4$ by $1$ .

$d = 4$

Step 2.1.1.4

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

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Step 2.1.1.4.1

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

$e = \frac{7}{4} - \frac{2^{2}}{4 (\frac{1}{4})}$

Step 2.1.1.4.2

Simplify the right side.

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Step 2.1.1.4.2.1

Simplify each term.

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Step 2.1.1.4.2.1.1

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

$e = \frac{7}{4} - \frac{4}{4 (\frac{1}{4})}$

Step 2.1.1.4.2.1.2

Combine $4$ and $\frac{1}{4}$ .

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

Step 2.1.1.4.2.1.3

Divide $4$ by $4$ .

$e = \frac{7}{4} - \frac{4}{1}$

Step 2.1.1.4.2.1.4

Divide $4$ by $1$ .

$e = \frac{7}{4} - 1 \cdot 4$

Step 2.1.1.4.2.1.5

Multiply $- 1$ by $4$ .

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

Step 2.1.1.4.2.2

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

$e = \frac{7}{4} - 4 \cdot \frac{4}{4}$

Step 2.1.1.4.2.3

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

$e = \frac{7}{4} + \frac{- 4 \cdot 4}{4}$

Step 2.1.1.4.2.4

Combine the numerators over the common denominator.

$e = \frac{7 - 4 \cdot 4}{4}$

Step 2.1.1.4.2.5

Simplify the numerator.

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Step 2.1.1.4.2.5.1

Multiply $- 4$ by $4$ .

$e = \frac{7 - 16}{4}$

Step 2.1.1.4.2.5.2

Subtract $16$ from $7$ .

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

Step 2.1.1.4.2.6

Move the negative in front of the fraction.

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

Step 2.1.1.5

Substitute the values of $a$ , $d$ , and $e$ into the vertex form $\frac{1}{4} {(x + 4)}^{2} - \frac{9}{4}$ .

$\frac{1}{4} {(x + 4)}^{2} - \frac{9}{4}$

Step 2.1.2

Set $y$ equal to the new right side.

$y = \frac{1}{4} \cdot {(x + 4)}^{2} - \frac{9}{4}$

Step 2.2

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

$a = \frac{1}{4}$

$h = - 4$

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

Step 2.3

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

Opens Up

Step 2.4

Find the vertex $(h, k)$ .

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

Step 2.5

Find $p$ , the distance from the vertex to the focus.

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Step 2.5.1

Find the distance from the vertex to a focus of the parabola by using the following formula.

$\frac{1}{4 a}$

Step 2.5.2

Substitute the value of $a$ into the formula.

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

Step 2.5.3

Simplify.

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Step 2.5.3.1

Combine $4$ and $\frac{1}{4}$ .

$\frac{1}{\frac{4}{4}}$

Step 2.5.3.2

Simplify by dividing numbers.

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Step 2.5.3.2.1

Divide $4$ by $4$ .

$\frac{1}{1}$

Step 2.5.3.2.2

Divide $1$ by $1$ .

$1$

Step 2.6

Find the focus.

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Step 2.6.1

The focus of a parabola can be found by adding $p$ to the y-coordinate $k$ if the parabola opens up or down.

$(h, k + p)$

Step 2.6.2

Substitute the known values of $h$ , $p$ , and $k$ into the formula and simplify.

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

Step 2.7

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

$x = - 4$

Step 2.8

Find the directrix.

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Step 2.8.1

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.

$y = k - p$

Step 2.8.2

Substitute the known values of $p$ and $k$ into the formula and simplify.

$y = - \frac{13}{4}$

Step 2.9

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

Direction: Opens Up

Vertex: $(- 4, - \frac{9}{4})$

Focus: $(- 4, - \frac{5}{4})$

Axis of Symmetry: $x = - 4$

Directrix: $y = - \frac{13}{4}$

Direction: Opens Up

Vertex: $(- 4, - \frac{9}{4})$

Focus: $(- 4, - \frac{5}{4})$

Axis of Symmetry: $x = - 4$

Directrix: $y = - \frac{13}{4}$

Step 3

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.

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Step 3.1

Replace the variable $x$ with $- 5$ in the expression.

$f (- 5) = \frac{{(- 5)}^{2}}{4} + 2 (- 5) + \frac{7}{4}$

Step 3.2

Simplify the result.

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Step 3.2.1

Combine fractions.

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Step 3.2.1.1

Combine the numerators over the common denominator.

$f (- 5) = 2 (- 5) + \frac{{(- 5)}^{2} + 7}{4}$

Step 3.2.1.2

Simplify the expression.

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Step 3.2.1.2.1

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

$f (- 5) = 2 (- 5) + \frac{25 + 7}{4}$

Step 3.2.1.2.2

Add $25$ and $7$ .

$f (- 5) = 2 (- 5) + \frac{32}{4}$

Step 3.2.2

Simplify each term.

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Step 3.2.2.1

Multiply $2$ by $- 5$ .

$f (- 5) = - 10 + \frac{32}{4}$

Step 3.2.2.2

Divide $32$ by $4$ .

$f (- 5) = - 10 + 8$

Step 3.2.3

Add $- 10$ and $8$ .

$f (- 5) = - 2$

Step 3.2.4

The final answer is $- 2$ .

$- 2$

Step 3.3

The $y$ value at $x = - 5$ is $- 2$ .

$y = - 2$

Step 3.4

Replace the variable $x$ with $- 6$ in the expression.

$f (- 6) = \frac{{(- 6)}^{2}}{4} + 2 (- 6) + \frac{7}{4}$

Step 3.5

Simplify the result.

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Step 3.5.1

Combine the numerators over the common denominator.

$f (- 6) = 2 (- 6) + \frac{{(- 6)}^{2} + 7}{4}$

Step 3.5.2

Simplify the expression.

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Step 3.5.2.1

Raise $- 6$ to the power of $2$ .

$f (- 6) = 2 (- 6) + \frac{36 + 7}{4}$

Step 3.5.2.2

Add $36$ and $7$ .

$f (- 6) = 2 (- 6) + \frac{43}{4}$

Step 3.5.2.3

Multiply $2$ by $- 6$ .

$f (- 6) = - 12 + \frac{43}{4}$

Step 3.5.3

To write $- 12$ as a fraction with a common denominator, multiply by $\frac{4}{4}$ .

$f (- 6) = - 12 \cdot \frac{4}{4} + \frac{43}{4}$

Step 3.5.4

Combine $- 12$ and $\frac{4}{4}$ .

$f (- 6) = \frac{- 12 \cdot 4}{4} + \frac{43}{4}$

Step 3.5.5

Combine the numerators over the common denominator.

$f (- 6) = \frac{- 12 \cdot 4 + 43}{4}$

Step 3.5.6

Simplify the numerator.

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Step 3.5.6.1

Multiply $- 12$ by $4$ .

$f (- 6) = \frac{- 48 + 43}{4}$

Step 3.5.6.2

Add $- 48$ and $43$ .

$f (- 6) = \frac{- 5}{4}$

Step 3.5.7

Move the negative in front of the fraction.

$f (- 6) = - \frac{5}{4}$

Step 3.5.8

The final answer is $- \frac{5}{4}$ .

$- \frac{5}{4}$

Step 3.6

The $y$ value at $x = - 6$ is $- \frac{5}{4}$ .

$y = - \frac{5}{4}$

Step 3.7

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

$f (- 3) = \frac{{(- 3)}^{2}}{4} + 2 (- 3) + \frac{7}{4}$

Step 3.8

Simplify the result.

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Step 3.8.1

Combine fractions.

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Step 3.8.1.1

Combine the numerators over the common denominator.

$f (- 3) = 2 (- 3) + \frac{{(- 3)}^{2} + 7}{4}$

Step 3.8.1.2

Simplify the expression.

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Step 3.8.1.2.1

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

$f (- 3) = 2 (- 3) + \frac{9 + 7}{4}$

Step 3.8.1.2.2

Add $9$ and $7$ .

$f (- 3) = 2 (- 3) + \frac{16}{4}$

Step 3.8.2

Simplify each term.

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Step 3.8.2.1

Multiply $2$ by $- 3$ .

$f (- 3) = - 6 + \frac{16}{4}$

Step 3.8.2.2

Divide $16$ by $4$ .

$f (- 3) = - 6 + 4$

Step 3.8.3

Add $- 6$ and $4$ .

$f (- 3) = - 2$

Step 3.8.4

The final answer is $- 2$ .

$- 2$

Step 3.9

The $y$ value at $x = - 3$ is $- 2$ .

$y = - 2$

Step 3.10

Replace the variable $x$ with $- 1$ in the expression.

$f (- 1) = \frac{{(- 1)}^{2}}{4} + 2 (- 1) + \frac{7}{4}$

Step 3.11

Simplify the result.

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Step 3.11.1

Combine fractions.

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Step 3.11.1.1

Combine the numerators over the common denominator.

$f (- 1) = 2 (- 1) + \frac{{(- 1)}^{2} + 7}{4}$

Step 3.11.1.2

Simplify the expression.

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Step 3.11.1.2.1

Raise $- 1$ to the power of $2$ .

$f (- 1) = 2 (- 1) + \frac{1 + 7}{4}$

Step 3.11.1.2.2

Add $1$ and $7$ .

$f (- 1) = 2 (- 1) + \frac{8}{4}$

Step 3.11.2

Simplify each term.

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Step 3.11.2.1

Multiply $2$ by $- 1$ .

$f (- 1) = - 2 + \frac{8}{4}$

Step 3.11.2.2

Divide $8$ by $4$ .

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

Step 3.11.3

Add $- 2$ and $2$ .

$f (- 1) = 0$

Step 3.11.4

The final answer is $0$ .

$0$

Step 3.12

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

$y = 0$

Step 3.13

Graph the parabola using its properties and the selected points.

$\begin{array}{c} x & y \\ - 6 & - \frac{5}{4} \\ - 5 & - 2 \\ - 4 & - \frac{9}{4} \\ - 3 & - 2 \\ - 1 & 0 \end{array}$

Step 4

Graph the parabola using its properties and the selected points.

Direction: Opens Up

Vertex: $(- 4, - \frac{9}{4})$

Focus: $(- 4, - \frac{5}{4})$

Axis of Symmetry: $x = - 4$

Directrix: $y = - \frac{13}{4}$

$\begin{array}{c} x & y \\ - 6 & - \frac{5}{4} \\ - 5 & - 2 \\ - 4 & - \frac{9}{4} \\ - 3 & - 2 \\ - 1 & 0 \end{array}$

Step 5