Solve by Completing the Square y^2-3y-10=0

$y^{2} - 3 y - 10 = 0$

Step 1

Add $10$ to both sides of the equation.

$y^{2} - 3 y = 10$

Step 2

To create a trinomial square on the left side of the equation, find a value that is equal to the square of half of $b$ .

${(\frac{b}{2})}^{2} = {(- \frac{3}{2})}^{2}$

Step 3

Add the term to each side of the equation.

$y^{2} - 3 y + {(- \frac{3}{2})}^{2} = 10 + {(- \frac{3}{2})}^{2}$

Step 4

Simplify the equation.

Simplify the left side.

Simplify each term.

Use the power rule ${(a b)}^{n} = a^{n} b^{n}$ to distribute the exponent.

Apply the product rule to $- \frac{3}{2}$ .

$y^{2} - 3 y + {(- 1)}^{2} {(\frac{3}{2})}^{2} = 10 + {(- \frac{3}{2})}^{2}$

Apply the product rule to $\frac{3}{2}$ .

$y^{2} - 3 y + {(- 1)}^{2} \frac{3^{2}}{2^{2}} = 10 + {(- \frac{3}{2})}^{2}$

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

$y^{2} - 3 y + 1 \frac{3^{2}}{2^{2}} = 10 + {(- \frac{3}{2})}^{2}$

Multiply $\frac{3^{2}}{2^{2}}$ by $1$ .

$y^{2} - 3 y + \frac{3^{2}}{2^{2}} = 10 + {(- \frac{3}{2})}^{2}$

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

$y^{2} - 3 y + \frac{9}{2^{2}} = 10 + {(- \frac{3}{2})}^{2}$

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

$y^{2} - 3 y + \frac{9}{4} = 10 + {(- \frac{3}{2})}^{2}$

Simplify the right side.

Simplify $10 + {(- \frac{3}{2})}^{2}$ .

Simplify each term.

Use the power rule ${(a b)}^{n} = a^{n} b^{n}$ to distribute the exponent.

Apply the product rule to $- \frac{3}{2}$ .

$y^{2} - 3 y + \frac{9}{4} = 10 + {(- 1)}^{2} {(\frac{3}{2})}^{2}$

Apply the product rule to $\frac{3}{2}$ .

$y^{2} - 3 y + \frac{9}{4} = 10 + {(- 1)}^{2} \frac{3^{2}}{2^{2}}$

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

$y^{2} - 3 y + \frac{9}{4} = 10 + 1 \frac{3^{2}}{2^{2}}$

Multiply $\frac{3^{2}}{2^{2}}$ by $1$ .

$y^{2} - 3 y + \frac{9}{4} = 10 + \frac{3^{2}}{2^{2}}$

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

$y^{2} - 3 y + \frac{9}{4} = 10 + \frac{9}{2^{2}}$

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

$y^{2} - 3 y + \frac{9}{4} = 10 + \frac{9}{4}$

To write $10$ as a fraction with a common denominator, multiply by $\frac{4}{4}$ .

$y^{2} - 3 y + \frac{9}{4} = 10 \cdot \frac{4}{4} + \frac{9}{4}$

Combine $10$ and $\frac{4}{4}$ .

$y^{2} - 3 y + \frac{9}{4} = \frac{10 \cdot 4}{4} + \frac{9}{4}$

Combine the numerators over the common denominator.

$y^{2} - 3 y + \frac{9}{4} = \frac{10 \cdot 4 + 9}{4}$

Simplify the numerator.

Multiply $10$ by $4$ .

$y^{2} - 3 y + \frac{9}{4} = \frac{40 + 9}{4}$

Add $40$ and $9$ .

$y^{2} - 3 y + \frac{9}{4} = \frac{49}{4}$

Step 5

Factor the perfect trinomial square into ${(y - \frac{3}{2})}^{2}$ .

${(y - \frac{3}{2})}^{2} = \frac{49}{4}$

Step 6

Solve the equation for $y$ .

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$y - \frac{3}{2} = \pm \sqrt{\frac{49}{4}}$

Simplify $\pm \sqrt{\frac{49}{4}}$ .

Rewrite $\sqrt{\frac{49}{4}}$ as $\frac{\sqrt{49}}{\sqrt{4}}$ .

$y - \frac{3}{2} = \pm \frac{\sqrt{49}}{\sqrt{4}}$

Simplify the numerator.

Rewrite $49$ as $7^{2}$ .

$y - \frac{3}{2} = \pm \frac{\sqrt{7^{2}}}{\sqrt{4}}$

Pull terms out from under the radical, assuming positive real numbers.

$y - \frac{3}{2} = \pm \frac{7}{\sqrt{4}}$

Simplify the denominator.

Rewrite $4$ as $2^{2}$ .

$y - \frac{3}{2} = \pm \frac{7}{\sqrt{2^{2}}}$

Pull terms out from under the radical, assuming positive real numbers.

$y - \frac{3}{2} = \pm \frac{7}{2}$

The complete solution is the result of both the positive and negative portions of the solution.

First, use the positive value of the $\pm$ to find the first solution.

$y - \frac{3}{2} = \frac{7}{2}$

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

Add $\frac{3}{2}$ to both sides of the equation.

$y = \frac{7}{2} + \frac{3}{2}$

Combine the numerators over the common denominator.

$y = \frac{7 + 3}{2}$

Add $7$ and $3$ .

$y = \frac{10}{2}$

Divide $10$ by $2$ .

$y = 5$

Next, use the negative value of the $\pm$ to find the second solution.

$y - \frac{3}{2} = - \frac{7}{2}$

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

Add $\frac{3}{2}$ to both sides of the equation.

$y = - \frac{7}{2} + \frac{3}{2}$

Combine the numerators over the common denominator.

$y = \frac{- 7 + 3}{2}$

Add $- 7$ and $3$ .

$y = \frac{- 4}{2}$

Divide $- 4$ by $2$ .

$y = - 2$

The complete solution is the result of both the positive and negative portions of the solution.

$y = 5, - 2$

Solve by Completing the Square y^2-3y-10=0

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