Algebra Examples

y = {(x - 2)}^{2} - 4

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

Step 1

Find the properties of the given parabola.

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Step 1.1

Use the vertex form,

y = a {(x - h)}^{2} + k

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

a

$a$ ,

h

$h$ , and

k

$k$ .

a = 1

$a = 1$

h = 2

$h = 2$

k = - 4

$k = - 4$

Step 1.2

Since the value of

a

$a$ is positive, the parabola opens up.

Opens Up

Step 1.3

Find the vertex

(h, k)

$(h, k)$ .

(2, - 4)

$(2, - 4)$

Step 1.4

Find

p

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

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Step 1.4.1

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

\frac{1}{4 a}

$\frac{1}{4 a}$

Step 1.4.2

Substitute the value of

a

$a$ into the formula.

\frac{1}{4 \cdot 1}

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

Step 1.4.3

Cancel the common factor of

1

$1$ .

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Step 1.4.3.1

Cancel the common factor.

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

Step 1.4.3.2

Rewrite the expression.

$\frac{1}{4}$

Step 1.5

Find the focus.

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Step 1.5.1

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 1.5.2

Substitute the known values of

$h$ ,

$p$ , and

$k$ into the formula and simplify.

$(2, - \frac{15}{4})$

Step 1.6

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

$x = 2$

Step 1.7

Find the directrix.

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Step 1.7.1

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 1.7.2

Substitute the known values of

$p$ and

$k$ into the formula and simplify.

$y = - \frac{17}{4}$

Step 1.8

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

Direction: Opens Up

Vertex:

$(2, - 4)$

Focus:

$(2, - \frac{15}{4})$

Axis of Symmetry:

$x = 2$

Directrix:

$y = - \frac{17}{4}$

Direction: Opens Up

Vertex:

$(2, - 4)$

Focus:

$(2, - \frac{15}{4})$

Axis of Symmetry:

$x = 2$

Directrix:

$y = - \frac{17}{4}$

Step 2

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 2.1

Replace the variable

$x$ with

$1$ in the expression.

$f (1) = {(1)}^{2} - 4 \cdot 1$

Step 2.2

Simplify the result.

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Step 2.2.1

Simplify each term.

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Step 2.2.1.1

One to any power is one.

$f (1) = 1 - 4 \cdot 1$

Step 2.2.1.2

Multiply

$- 4$ by

$1$ .

$f (1) = 1 - 4$

Step 2.2.2

Subtract

$4$ from

$1$ .

$f (1) = - 3$

Step 2.2.3

The final answer is

$- 3$ .

$- 3$

Step 2.3

The

$y$ value at

$x = 1$ is

$- 3$ .

$y = - 3$

Step 2.4

Replace the variable

$x$ with

$0$ in the expression.

$f (0) = {(0)}^{2} - 4 \cdot 0$

Step 2.5

Simplify the result.

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Step 2.5.1

Simplify each term.

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Step 2.5.1.1

Raising

$0$ to any positive power yields

$0$ .

$f (0) = 0 - 4 \cdot 0$

Step 2.5.1.2

Multiply

$- 4$ by

$0$ .

$f (0) = 0 + 0$

Step 2.5.2

Add

$0$ and

$0$ .

$f (0) = 0$

Step 2.5.3

The final answer is

$0$ .

$0$

Step 2.6

The

$y$ value at

$x = 0$ is

$0$ .

$y = 0$

Step 2.7

Replace the variable

$x$ with

$3$ in the expression.

$f (3) = {(3)}^{2} - 4 \cdot 3$

Step 2.8

Simplify the result.

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Step 2.8.1

Simplify each term.

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Step 2.8.1.1

Raise

$3$ to the power of

$2$ .

$f (3) = 9 - 4 \cdot 3$

Step 2.8.1.2

Multiply

$- 4$ by

$3$ .

$f (3) = 9 - 12$

Step 2.8.2

Subtract

$12$ from

$9$ .

$f (3) = - 3$

Step 2.8.3

The final answer is

$- 3$ .

$- 3$

Step 2.9

The

$y$ value at

$x = 3$ is

$- 3$ .

$y = - 3$

Step 2.10

Replace the variable

$x$ with

$4$ in the expression.

$f (4) = {(4)}^{2} - 4 \cdot 4$

Step 2.11

Simplify the result.

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Step 2.11.1

Simplify each term.

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Step 2.11.1.1

Raise

$4$ to the power of

$2$ .

$f (4) = 16 - 4 \cdot 4$

Step 2.11.1.2

Multiply

$- 4$ by

$4$ .

$f (4) = 16 - 16$

Step 2.11.2

Subtract

$16$ from

$16$ .

$f (4) = 0$

Step 2.11.3

The final answer is

$0$ .

$0$

Step 2.12

The

$y$ value at

$x = 4$ is

$0$ .

$y = 0$

Step 2.13

Graph the parabola using its properties and the selected points.

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

Step 3

Graph the parabola using its properties and the selected points.

Direction: Opens Up

Vertex:

$(2, - 4)$

Focus:

$(2, - \frac{15}{4})$

Axis of Symmetry:

$x = 2$

Directrix:

$y = - \frac{17}{4}$

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

Step 4