Precalculus Examples

$y^{2} + 6 y + 8 x + 25 = 0$

Step 1

Rewrite the equation in vertex form.

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Step 1.1

Isolate $x$ to the left side of the equation.

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Step 1.1.1

Move all terms not containing $x$ to the right side of the equation.

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Step 1.1.1.1

Subtract $y^{2}$ from both sides of the equation.

$6 y + 8 x + 25 = - y^{2}$

Step 1.1.1.2

Subtract $6 y$ from both sides of the equation.

$8 x + 25 = - y^{2} - 6 y$

Step 1.1.1.3

Subtract $25$ from both sides of the equation.

$8 x = - y^{2} - 6 y - 25$

Step 1.1.2

Divide each term in $8 x = - y^{2} - 6 y - 25$ by $8$ and simplify.

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Step 1.1.2.1

Divide each term in $8 x = - y^{2} - 6 y - 25$ by $8$ .

$\frac{8 x}{8} = \frac{- y^{2}}{8} + \frac{- 6 y}{8} + \frac{- 25}{8}$

Step 1.1.2.2

Simplify the left side.

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Step 1.1.2.2.1

Cancel the common factor of $8$ .

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Step 1.1.2.2.1.1

Cancel the common factor.

$\frac{8 x}{8} = \frac{- y^{2}}{8} + \frac{- 6 y}{8} + \frac{- 25}{8}$

Step 1.1.2.2.1.2

Divide $x$ by $1$ .

$x = \frac{- y^{2}}{8} + \frac{- 6 y}{8} + \frac{- 25}{8}$

Step 1.1.2.3

Simplify the right side.

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Step 1.1.2.3.1

Simplify each term.

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Step 1.1.2.3.1.1

Move the negative in front of the fraction.

$x = - \frac{y^{2}}{8} + \frac{- 6 y}{8} + \frac{- 25}{8}$

Step 1.1.2.3.1.2

Cancel the common factor of $- 6$ and $8$ .

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Step 1.1.2.3.1.2.1

Factor $2$ out of $- 6 y$ .

$x = - \frac{y^{2}}{8} + \frac{2 (- 3 y)}{8} + \frac{- 25}{8}$

Step 1.1.2.3.1.2.2

Cancel the common factors.

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Step 1.1.2.3.1.2.2.1

Factor $2$ out of $8$ .

$x = - \frac{y^{2}}{8} + \frac{2 (- 3 y)}{2 (4)} + \frac{- 25}{8}$

Step 1.1.2.3.1.2.2.2

Cancel the common factor.

$x = - \frac{y^{2}}{8} + \frac{2 (- 3 y)}{2 \cdot 4} + \frac{- 25}{8}$

Step 1.1.2.3.1.2.2.3

Rewrite the expression.

$x = - \frac{y^{2}}{8} + \frac{- 3 y}{4} + \frac{- 25}{8}$

Step 1.1.2.3.1.3

Move the negative in front of the fraction.

$x = - \frac{y^{2}}{8} - \frac{3 y}{4} + \frac{- 25}{8}$

Step 1.1.2.3.1.4

Move the negative in front of the fraction.

$x = - \frac{y^{2}}{8} - \frac{3 y}{4} - \frac{25}{8}$

Step 1.2

Complete the square for $- \frac{y^{2}}{8} - \frac{3 y}{4} - \frac{25}{8}$ .

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Step 1.2.1

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

$a = - \frac{1}{8}$

$b = - \frac{3}{4}$

$c = - \frac{25}{8}$

Step 1.2.2

Consider the vertex form of a parabola.

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

Step 1.2.3

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

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Step 1.2.3.1

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

$d = \frac{- \frac{3}{4}}{2 (- \frac{1}{8})}$

Step 1.2.3.2

Simplify the right side.

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Step 1.2.3.2.1

Dividing two negative values results in a positive value.

$d = \frac{\frac{3}{4}}{2 (\frac{1}{8})}$

Step 1.2.3.2.2

Multiply the numerator by the reciprocal of the denominator.

$d = \frac{3}{4} \cdot \frac{1}{2 (\frac{1}{8})}$

Step 1.2.3.2.3

Combine $2$ and $\frac{1}{8}$ .

$d = \frac{3}{4} \cdot \frac{1}{\frac{2}{8}}$

Step 1.2.3.2.4

Cancel the common factor of $2$ and $8$ .

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Step 1.2.3.2.4.1

Factor $2$ out of $2$ .

$d = \frac{3}{4} \cdot \frac{1}{\frac{2 (1)}{8}}$

Step 1.2.3.2.4.2

Cancel the common factors.

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Step 1.2.3.2.4.2.1

Factor $2$ out of $8$ .

$d = \frac{3}{4} \cdot \frac{1}{\frac{2 \cdot 1}{2 \cdot 4}}$

Step 1.2.3.2.4.2.2

Cancel the common factor.

$d = \frac{3}{4} \cdot \frac{1}{\frac{2 \cdot 1}{2 \cdot 4}}$

Step 1.2.3.2.4.2.3

Rewrite the expression.

$d = \frac{3}{4} \cdot \frac{1}{\frac{1}{4}}$

Step 1.2.3.2.5

Multiply the numerator by the reciprocal of the denominator.

$d = \frac{3}{4} (1 \cdot 4)$

Step 1.2.3.2.6

Cancel the common factor of $4$ .

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Step 1.2.3.2.6.1

Factor $4$ out of $1 \cdot 4$ .

$d = \frac{3}{4} (4 \cdot 1)$

Step 1.2.3.2.6.2

Cancel the common factor.

$d = \frac{3}{4} (4 \cdot 1)$

Step 1.2.3.2.6.3

Rewrite the expression.

$d = 3$

Step 1.2.4

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

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Step 1.2.4.1

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

$e = - \frac{25}{8} - \frac{{(- \frac{3}{4})}^{2}}{4 (- \frac{1}{8})}$

Step 1.2.4.2

Simplify the right side.

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Step 1.2.4.2.1

Simplify each term.

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Step 1.2.4.2.1.1

Simplify the numerator.

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Step 1.2.4.2.1.1.1

Apply the product rule to $- \frac{3}{4}$ .

$e = - \frac{25}{8} - \frac{{(- 1)}^{2} {(\frac{3}{4})}^{2}}{4 (- \frac{1}{8})}$

Step 1.2.4.2.1.1.2

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

$e = - \frac{25}{8} - \frac{1 {(\frac{3}{4})}^{2}}{4 (- \frac{1}{8})}$

Step 1.2.4.2.1.1.3

Apply the product rule to $\frac{3}{4}$ .

$e = - \frac{25}{8} - \frac{1 \frac{3^{2}}{4^{2}}}{4 (- \frac{1}{8})}$

Step 1.2.4.2.1.1.4

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

$e = - \frac{25}{8} - \frac{1 \frac{9}{4^{2}}}{4 (- \frac{1}{8})}$

Step 1.2.4.2.1.1.5

Raise $4$ to the power of $2$ .

$e = - \frac{25}{8} - \frac{1 (\frac{9}{16})}{4 (- \frac{1}{8})}$

Step 1.2.4.2.1.1.6

Multiply $\frac{9}{16}$ by $1$ .

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{4 (- \frac{1}{8})}$

Step 1.2.4.2.1.2

Simplify the denominator.

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Step 1.2.4.2.1.2.1

Multiply $- 1$ by $4$ .

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{- 4 (\frac{1}{8})}$

Step 1.2.4.2.1.2.2

Combine $- 4$ and $\frac{1}{8}$ .

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{\frac{- 4}{8}}$

Step 1.2.4.2.1.3

Reduce the expression by cancelling the common factors.

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Step 1.2.4.2.1.3.1

Cancel the common factor of $- 4$ and $8$ .

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Step 1.2.4.2.1.3.1.1

Factor $4$ out of $- 4$ .

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{\frac{4 (- 1)}{8}}$

Step 1.2.4.2.1.3.1.2

Cancel the common factors.

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Step 1.2.4.2.1.3.1.2.1

Factor $4$ out of $8$ .

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{\frac{4 \cdot - 1}{4 \cdot 2}}$

Step 1.2.4.2.1.3.1.2.2

Cancel the common factor.

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{\frac{4 \cdot - 1}{4 \cdot 2}}$

Step 1.2.4.2.1.3.1.2.3

Rewrite the expression.

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{\frac{- 1}{2}}$

Step 1.2.4.2.1.3.2

Move the negative in front of the fraction.

$e = - \frac{25}{8} - \frac{\frac{9}{16}}{- \frac{1}{2}}$

Step 1.2.4.2.1.4

Multiply the numerator by the reciprocal of the denominator.

$e = - \frac{25}{8} - (\frac{9}{16} (- 1 \cdot 2))$

Step 1.2.4.2.1.5

Cancel the common factor of $2$ .

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Step 1.2.4.2.1.5.1

Factor $2$ out of $16$ .

$e = - \frac{25}{8} - (\frac{9}{2 (8)} (- 1 \cdot 2))$

Step 1.2.4.2.1.5.2

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

$e = - \frac{25}{8} - (\frac{9}{2 (8)} (2 \cdot - 1))$

Step 1.2.4.2.1.5.3

Cancel the common factor.

$e = - \frac{25}{8} - (\frac{9}{2 \cdot 8} (2 \cdot - 1))$

Step 1.2.4.2.1.5.4

Rewrite the expression.

$e = - \frac{25}{8} - (\frac{9}{8} \cdot - 1)$

Step 1.2.4.2.1.6

Combine $\frac{9}{8}$ and $- 1$ .

$e = - \frac{25}{8} - \frac{9 \cdot - 1}{8}$

Step 1.2.4.2.1.7

Multiply $9$ by $- 1$ .

$e = - \frac{25}{8} - \frac{- 9}{8}$

Step 1.2.4.2.1.8

Move the negative in front of the fraction.

$e = - \frac{25}{8} - - \frac{9}{8}$

Step 1.2.4.2.1.9

Multiply $- - \frac{9}{8}$ .

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Step 1.2.4.2.1.9.1

Multiply $- 1$ by $- 1$ .

$e = - \frac{25}{8} + 1 (\frac{9}{8})$

Step 1.2.4.2.1.9.2

Multiply $\frac{9}{8}$ by $1$ .

$e = - \frac{25}{8} + \frac{9}{8}$

Step 1.2.4.2.2

Combine the numerators over the common denominator.

$e = \frac{- 25 + 9}{8}$

Step 1.2.4.2.3

Add $- 25$ and $9$ .

$e = \frac{- 16}{8}$

Step 1.2.4.2.4

Divide $- 16$ by $8$ .

$e = - 2$

Step 1.2.5

Substitute the values of $a$ , $d$ , and $e$ into the vertex form $- \frac{1}{8} {(y + 3)}^{2} - 2$ .

$- \frac{1}{8} {(y + 3)}^{2} - 2$

Step 1.3

Set $x$ equal to the new right side.

$x = - \frac{1}{8} \cdot {(y + 3)}^{2} - 2$

Step 2

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

$a = - \frac{1}{8}$

$h = - 2$

$k = - 3$

Step 3

Since the value of $a$ is negative, the parabola opens left.

Opens Left

Step 4

Find the vertex $(h, k)$ .

$(- 2, - 3)$

Step 5

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

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Step 5.1

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

$\frac{1}{4 a}$

Step 5.2

Substitute the value of $a$ into the formula.

$\frac{1}{4 \cdot (- \frac{1}{8})}$

Step 5.3

Simplify.

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Step 5.3.1

Cancel the common factor of $1$ and $- 1$ .

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Step 5.3.1.1

Rewrite $1$ as $- 1 (- 1)$ .

$\frac{- 1 (- 1)}{4 \cdot (- \frac{1}{8})}$

Step 5.3.1.2

Move the negative in front of the fraction.

$- \frac{1}{4 (\frac{1}{8})}$

Step 5.3.2

Combine $4$ and $\frac{1}{8}$ .

$- \frac{1}{\frac{4}{8}}$

Step 5.3.3

Cancel the common factor of $4$ and $8$ .

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Step 5.3.3.1

Factor $4$ out of $4$ .

$- \frac{1}{\frac{4 (1)}{8}}$

Step 5.3.3.2

Cancel the common factors.

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Step 5.3.3.2.1

Factor $4$ out of $8$ .

$- \frac{1}{\frac{4 \cdot 1}{4 \cdot 2}}$

Step 5.3.3.2.2

Cancel the common factor.

$- \frac{1}{\frac{4 \cdot 1}{4 \cdot 2}}$

Step 5.3.3.2.3

Rewrite the expression.

$- \frac{1}{\frac{1}{2}}$

Step 5.3.4

Multiply the numerator by the reciprocal of the denominator.

$- (1 \cdot 2)$

Step 5.3.5

Multiply $- (1 \cdot 2)$ .

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Step 5.3.5.1

Multiply $2$ by $1$ .

$- 1 \cdot 2$

Step 5.3.5.2

Multiply $- 1$ by $2$ .

$- 2$

Step 6

Find the focus.

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Step 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 6.2

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

$(- 4, - 3)$

Step 7

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

$y = - 3$

Step 8

Find the directrix.

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Step 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 8.2

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

$x = 0$

Step 9

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

Direction: Opens Left

Vertex: $(- 2, - 3)$

Focus: $(- 4, - 3)$

Axis of Symmetry: $y = - 3$

Directrix: $x = 0$

Step 10