Precalculus Examples

$x - 4 = y^{2}$

Step 1

Add $4$ to both sides of the equation.

$x = y^{2} + 4$

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 $y^{2} + 4$ .

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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 $c$ .

$a = 1$

$b = 0$

$c = 4$

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

$d = \frac{0}{2 \cdot 1}$

Step 2.1.1.3.2

Cancel the common factor of $0$ and $2$ .

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Step 2.1.1.3.2.1

Factor $2$ out of $0$ .

$d = \frac{2 (0)}{2 \cdot 1}$

Step 2.1.1.3.2.2

Cancel the common factors.

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Step 2.1.1.3.2.2.1

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

$d = \frac{2 (0)}{2 (1)}$

Step 2.1.1.3.2.2.2

Cancel the common factor.

$d = \frac{2 \cdot 0}{2 \cdot 1}$

Step 2.1.1.3.2.2.3

Rewrite the expression.

$d = \frac{0}{1}$

Step 2.1.1.3.2.2.4

Divide $0$ by $1$ .

$d = 0$

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

$e = 4 - \frac{0^{2}}{4 \cdot 1}$

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

Raising $0$ to any positive power yields $0$ .

$e = 4 - \frac{0}{4 \cdot 1}$

Step 2.1.1.4.2.1.2

Multiply $4$ by $1$ .

$e = 4 - \frac{0}{4}$

Step 2.1.1.4.2.1.3

Divide $0$ by $4$ .

$e = 4 - 0$

Step 2.1.1.4.2.1.4

Multiply $- 1$ by $0$ .

$e = 4 + 0$

Step 2.1.1.4.2.2

Add $4$ and $0$ .

$e = 4$

Step 2.1.1.5

Substitute the values of $a$ , $d$ , and $e$ into the vertex form ${(y + 0)}^{2} + 4$ .

${(y + 0)}^{2} + 4$

Step 2.1.2

Set $x$ equal to the new right side.

$x = {(y + 0)}^{2} + 4$

Step 2.2

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

$a = 1$

$h = 4$

$k = 0$

Step 2.3

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

Opens Right

Step 2.4

Find the vertex $(h, k)$ .

$(4, 0)$

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.

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

Step 2.5.3

Cancel the common factor of $1$ .

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Step 2.5.3.1

Cancel the common factor.

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

Step 2.5.3.2

Rewrite the expression.

$\frac{1}{4}$

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 x-coordinate $h$ if the parabola opens left or right.

$(h + p, k)$

Step 2.6.2

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

$(\frac{17}{4}, 0)$

Step 2.7

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

$y = 0$

Step 2.8

Find the directrix.

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Step 2.8.1

The directrix of a parabola is the vertical line found by subtracting $p$ from the x-coordinate $h$ of the vertex if the parabola opens left or right.

$x = h - p$

Step 2.8.2

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

$x = \frac{15}{4}$

Step 2.9

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

Direction: Opens Right

Vertex: $(4, 0)$

Focus: $(\frac{17}{4}, 0)$

Axis of Symmetry: $y = 0$

Directrix: $x = \frac{15}{4}$

Direction: Opens Right

Vertex: $(4, 0)$

Focus: $(\frac{17}{4}, 0)$

Axis of Symmetry: $y = 0$

Directrix: $x = \frac{15}{4}$

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

Substitute the $x$ value $5$ into $f (x) = \sqrt{x - 4}$ . In this case, the point is $(5, 1)$ .

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Step 3.1.1

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

$f (5) = \sqrt{(5) - 4}$

Step 3.1.2

Simplify the result.

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Step 3.1.2.1

Subtract $4$ from $5$ .

$f (5) = \sqrt{1}$

Step 3.1.2.2

Any root of $1$ is $1$ .

$f (5) = 1$

Step 3.1.2.3

The final answer is $1$ .

$y = 1$

Step 3.1.3

Convert $1$ to decimal.

$= 1$

Step 3.2

Substitute the $x$ value $5$ into $f (x) = - \sqrt{x - 4}$ . In this case, the point is $(5, - 1)$ .

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Step 3.2.1

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

$f (5) = - \sqrt{(5) - 4}$

Step 3.2.2

Simplify the result.

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Step 3.2.2.1

Subtract $4$ from $5$ .

$f (5) = - \sqrt{1}$

Step 3.2.2.2

Any root of $1$ is $1$ .

$f (5) = - 1 \cdot 1$

Step 3.2.2.3

Multiply $- 1$ by $1$ .

$f (5) = - 1$

Step 3.2.2.4

The final answer is $- 1$ .

$y = - 1$

Step 3.2.3

Convert $- 1$ to decimal.

$= - 1$

Step 3.3

Substitute the $x$ value $6$ into $f (x) = \sqrt{x - 4}$ . In this case, the point is $(6, 1.41421356)$ .

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Step 3.3.1

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

$f (6) = \sqrt{(6) - 4}$

Step 3.3.2

Simplify the result.

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Step 3.3.2.1

Subtract $4$ from $6$ .

$f (6) = \sqrt{2}$

Step 3.3.2.2

The final answer is $\sqrt{2}$ .

$y = \sqrt{2}$

Step 3.3.3

Convert $\sqrt{2}$ to decimal.

$= 1.41421356$

Step 3.4

Substitute the $x$ value $6$ into $f (x) = - \sqrt{x - 4}$ . In this case, the point is $(6, - 1.41421356)$ .

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Step 3.4.1

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

$f (6) = - \sqrt{(6) - 4}$

Step 3.4.2

Simplify the result.

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Step 3.4.2.1

Subtract $4$ from $6$ .

$f (6) = - \sqrt{2}$

Step 3.4.2.2

The final answer is $- \sqrt{2}$ .

$y = - \sqrt{2}$

Step 3.4.3

Convert $- \sqrt{2}$ to decimal.

$= - 1.41421356$

Step 3.5

Graph the parabola using its properties and the selected points.

$\begin{array}{c} x & y \\ 4 & 0 \\ 5 & 1 \\ 5 & - 1 \\ 6 & 1.41 \\ 6 & - 1.41 \end{array}$

Step 4

Graph the parabola using its properties and the selected points.

Direction: Opens Right

Vertex: $(4, 0)$

Focus: $(\frac{17}{4}, 0)$

Axis of Symmetry: $y = 0$

Directrix: $x = \frac{15}{4}$

$\begin{array}{c} x & y \\ 4 & 0 \\ 5 & 1 \\ 5 & - 1 \\ 6 & 1.41 \\ 6 & - 1.41 \end{array}$

Step 5