Finite Math Examples

$\frac{1}{x + 5} + \frac{1}{x} = \frac{1}{15}$

Step 1

Find the LCD of the terms in the equation.

Tap for more steps...

Step 1.1

Finding the LCD of a list of values is the same as finding the LCM of the denominators of those values.

$x + 5, x, 15$

Step 1.2

Since $x + 5, x, 15$ contains both numbers and variables, there are four steps to find the LCM. Find LCM for the numeric, variable, and compound variable parts. Then, multiply them all together.

Steps to find the LCM for $x + 5, x, 15$ are:

1. Find the LCM for the numeric part $1, 1, 15$ .

2. Find the LCM for the variable part $x^{1}$ .

3. Find the LCM for the compound variable part $x + 5$ .

4. Multiply each LCM together.

Step 1.3

The LCM is the smallest positive number that all of the numbers divide into evenly.

1. List the prime factors of each number.

2. Multiply each factor the greatest number of times it occurs in either number.

Step 1.4

The number $1$ is not a prime number because it only has one positive factor, which is itself.

Not prime

Step 1.5

$15$ has factors of $3$ and $5$ .

$3 \cdot 5$

Step 1.6

Multiply $3$ by $5$ .

$15$

Step 1.7

The factor for $x^{1}$ is $x$ itself.

$x^{1} = x$

$x$ occurs $1$ time.

Step 1.8

The LCM of $x^{1}$ is the result of multiplying all prime factors the greatest number of times they occur in either term.

$x$

Step 1.9

The factor for $x + 5$ is $x + 5$ itself.

$(x + 5) = x + 5$

$(x + 5)$ occurs $1$ time.

Step 1.10

The LCM of $x + 5$ is the result of multiplying all factors the greatest number of times they occur in either term.

$x + 5$

Step 1.11

The Least Common Multiple $LCM$ of some numbers is the smallest number that the numbers are factors of.

$15 x (x + 5)$

Step 2

Multiply each term in $\frac{1}{x + 5} + \frac{1}{x} = \frac{1}{15}$ by $15 x (x + 5)$ to eliminate the fractions.

Tap for more steps...

Step 2.1

Multiply each term in $\frac{1}{x + 5} + \frac{1}{x} = \frac{1}{15}$ by $15 x (x + 5)$ .

$\frac{1}{x + 5} (15 x (x + 5)) + \frac{1}{x} (15 x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2

Simplify the left side.

Tap for more steps...

Step 2.2.1

Simplify each term.

Tap for more steps...

Step 2.2.1.1

Rewrite using the commutative property of multiplication.

$15 \frac{1}{x + 5} (x (x + 5)) + \frac{1}{x} (15 x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.2

Combine $15$ and $\frac{1}{x + 5}$ .

$\frac{15}{x + 5} (x (x + 5)) + \frac{1}{x} (15 x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.3

Cancel the common factor of $x + 5$ .

Tap for more steps...

Step 2.2.1.3.1

Factor $x + 5$ out of $x (x + 5)$ .

$\frac{15}{x + 5} ((x + 5) x) + \frac{1}{x} (15 x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.3.2

Cancel the common factor.

$\frac{15}{x + 5} ((x + 5) x) + \frac{1}{x} (15 x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.3.3

Rewrite the expression.

$15 x + \frac{1}{x} (15 x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.4

Rewrite using the commutative property of multiplication.

$15 x + 15 \frac{1}{x} (x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.5

Combine $15$ and $\frac{1}{x}$ .

$15 x + \frac{15}{x} (x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.6

Cancel the common factor of $x$ .

Tap for more steps...

Step 2.2.1.6.1

Cancel the common factor.

$15 x + \frac{15}{x} (x (x + 5)) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.6.2

Rewrite the expression.

$15 x + 15 (x + 5) = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.7

Apply the distributive property.

$15 x + 15 x + 15 \cdot 5 = \frac{1}{15} (15 x (x + 5))$

Step 2.2.1.8

Multiply $15$ by $5$ .

$15 x + 15 x + 75 = \frac{1}{15} (15 x (x + 5))$

Step 2.2.2

Add $15 x$ and $15 x$ .

$30 x + 75 = \frac{1}{15} (15 x (x + 5))$

Step 2.3

Simplify the right side.

Tap for more steps...

Step 2.3.1

Cancel the common factor of $15$ .

Tap for more steps...

Step 2.3.1.1

Factor $15$ out of $15 x (x + 5)$ .

$30 x + 75 = \frac{1}{15} (15 (x (x + 5)))$

Step 2.3.1.2

Cancel the common factor.

$30 x + 75 = \frac{1}{15} (15 (x (x + 5)))$

Step 2.3.1.3

Rewrite the expression.

$30 x + 75 = x (x + 5)$

Step 2.3.2

Apply the distributive property.

$30 x + 75 = x \cdot x + x \cdot 5$

Step 2.3.3

Simplify the expression.

Tap for more steps...

Step 2.3.3.1

Multiply $x$ by $x$ .

$30 x + 75 = x^{2} + x \cdot 5$

Step 2.3.3.2

Move $5$ to the left of $x$ .

$30 x + 75 = x^{2} + 5 x$

Step 3

Solve the equation.

Tap for more steps...

Step 3.1

Since $x$ is on the right side of the equation, switch the sides so it is on the left side of the equation.

$x^{2} + 5 x = 30 x + 75$

Step 3.2

Move all terms containing $x$ to the left side of the equation.

Tap for more steps...

Step 3.2.1

Subtract $30 x$ from both sides of the equation.

$x^{2} + 5 x - 30 x = 75$

Step 3.2.2

Subtract $30 x$ from $5 x$ .

$x^{2} - 25 x = 75$

Step 3.3

Subtract $75$ from both sides of the equation.

$x^{2} - 25 x - 75 = 0$

Step 3.4

Use the quadratic formula to find the solutions.

$\frac{- b \pm \sqrt{b^{2} - 4 (a c)}}{2 a}$

Step 3.5

Substitute the values $a = 1$ , $b = - 25$ , and $c = - 75$ into the quadratic formula and solve for $x$ .

$\frac{25 \pm \sqrt{{(- 25)}^{2} - 4 \cdot (1 \cdot - 75)}}{2 \cdot 1}$

Step 3.6

Simplify.

Tap for more steps...

Step 3.6.1

Simplify the numerator.

Tap for more steps...

Step 3.6.1.1

Raise $- 25$ to the power of $2$ .

$x = \frac{25 \pm \sqrt{625 - 4 \cdot 1 \cdot - 75}}{2 \cdot 1}$

Step 3.6.1.2

Multiply $- 4 \cdot 1 \cdot - 75$ .

Tap for more steps...

Step 3.6.1.2.1

Multiply $- 4$ by $1$ .

$x = \frac{25 \pm \sqrt{625 - 4 \cdot - 75}}{2 \cdot 1}$

Step 3.6.1.2.2

Multiply $- 4$ by $- 75$ .

$x = \frac{25 \pm \sqrt{625 + 300}}{2 \cdot 1}$

Step 3.6.1.3

Add $625$ and $300$ .

$x = \frac{25 \pm \sqrt{925}}{2 \cdot 1}$

Step 3.6.1.4

Rewrite $925$ as $5^{2} \cdot 37$ .

Tap for more steps...

Step 3.6.1.4.1

Factor $25$ out of $925$ .

$x = \frac{25 \pm \sqrt{25 (37)}}{2 \cdot 1}$

Step 3.6.1.4.2

Rewrite $25$ as $5^{2}$ .

$x = \frac{25 \pm \sqrt{5^{2} \cdot 37}}{2 \cdot 1}$

Step 3.6.1.5

Pull terms out from under the radical.

$x = \frac{25 \pm 5 \sqrt{37}}{2 \cdot 1}$

Step 3.6.2

Multiply $2$ by $1$ .

$x = \frac{25 \pm 5 \sqrt{37}}{2}$

Step 3.7

The final answer is the combination of both solutions.

$x = \frac{25 + 5 \sqrt{37}}{2}, \frac{25 - 5 \sqrt{37}}{2}$

Step 4

The result can be shown in multiple forms.

Exact Form:

$x = \frac{25 + 5 \sqrt{37}}{2}, \frac{25 - 5 \sqrt{37}}{2}$

Decimal Form:

$x = 27.70690632 \dots, - 2.70690632 \dots$