Precalculus Examples

$2 \log (x) - \log (5) = \log (180)$

Step 1

Move all the terms containing a logarithm to the left side of the equation.

$2 \log (x) - \log (5) - \log (180) = 0$

Step 2

Simplify the left side.

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Step 2.1

Simplify $2 \log (x) - \log (5) - \log (180)$ .

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Step 2.1.1

Simplify $2 \log (x)$ by moving $2$ inside the logarithm.

$\log (x^{2}) - \log (5) - \log (180) = 0$

Step 2.1.2

Use the quotient property of logarithms, $\log_{b} (x) - \log_{b} (y) = \log_{b} (\frac{x}{y})$ .

$\log (\frac{x^{2}}{5}) - \log (180) = 0$

Step 2.1.3

Use the quotient property of logarithms, $\log_{b} (x) - \log_{b} (y) = \log_{b} (\frac{x}{y})$ .

$\log (\frac{\frac{x^{2}}{5}}{180}) = 0$

Step 2.1.4

Multiply the numerator by the reciprocal of the denominator.

$\log (\frac{x^{2}}{5} \cdot \frac{1}{180}) = 0$

Step 2.1.5

Combine.

$\log (\frac{x^{2} \cdot 1}{5 \cdot 180}) = 0$

Step 2.1.6

Multiply.

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Step 2.1.6.1

Multiply $x^{2}$ by $1$ .

$\log (\frac{x^{2}}{5 \cdot 180}) = 0$

Step 2.1.6.2

Multiply $5$ by $180$ .

$\log (\frac{x^{2}}{900}) = 0$

Step 3

Rewrite $\log (\frac{x^{2}}{900}) = 0$ in exponential form using the definition of a logarithm. If $x$ and $b$ are positive real numbers and $b \neq 1$ , then $\log_{b} (x) = y$ is equivalent to $b^{y} = x$ .

$10^{0} = \frac{x^{2}}{900}$

Step 4

Solve for $x$ .

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Step 4.1

Rewrite the equation as $\frac{x^{2}}{900} = 10^{0}$ .

$\frac{x^{2}}{900} = 10^{0}$

Step 4.2

Multiply both sides of the equation by $900$ .

$900 \frac{x^{2}}{900} = 900 \cdot 10^{0}$

Step 4.3

Simplify both sides of the equation.

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Step 4.3.1

Simplify the left side.

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Step 4.3.1.1

Cancel the common factor of $900$ .

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Step 4.3.1.1.1

Cancel the common factor.

$900 \frac{x^{2}}{900} = 900 \cdot 10^{0}$

Step 4.3.1.1.2

Rewrite the expression.

$x^{2} = 900 \cdot 10^{0}$

Step 4.3.2

Simplify the right side.

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Step 4.3.2.1

Move the decimal point in $900$ to the left by $2$ places and increase the power of $10^{0}$ by $2$ .

$x^{2} = 9 \cdot 10^{2}$

Step 4.4

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

$x = \pm \sqrt{9 \cdot 10^{2}}$

Step 4.5

Simplify $\pm \sqrt{9 \cdot 10^{2}}$ .

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Step 4.5.1

Rewrite $\sqrt{9 \cdot 10^{2}}$ as $\sqrt{9} \cdot \sqrt{10^{2}}$ .

$x = \pm \sqrt{9} \cdot \sqrt{10^{2}}$

Step 4.5.2

Evaluate the root.

$x = \pm 3 \cdot \sqrt{10^{2}}$

Step 4.5.3

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

$x = \pm 3 \cdot 10$

Step 4.5.4

Raise $10$ to the power of $1$ .

$x = \pm 3 \cdot 10^{1}$

Step 4.6

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

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Step 4.6.1

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

$x = 3 \cdot 10^{1}$

Step 4.6.2

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

$x = - 3 \cdot 10^{1}$

Step 4.6.3

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

$x = 3 \cdot 10^{1}, - 3 \cdot 10^{1}$

Step 5

Exclude the solutions that do not make $2 \log (x) - \log (5) = \log (180)$ true.

$x = 3 \cdot 10^{1}$

Step 6

The result can be shown in multiple forms.

Scientific Notation:

$x = 3 \cdot 10^{1}$

Expanded Form:

$x = 30$