Expand Using the Binomial Theorem (x+1/x)^3

${(x + \frac{1}{x})}^{3}$

Step 1

Use the binomial expansion theorem to find each term. The binomial theorem states ${(a + b)}^{n} = \sum_{k = 0}^{n} n C k \cdot (a^{n - k} b^{k})$ .

$\sum_{k = 0}^{3} \frac{3!}{(3 - k)! k!} \cdot {(x)}^{3 - k} \cdot {(\frac{1}{x})}^{k}$

Step 2

Expand the summation.

$\frac{3!}{(3 - 0)! 0!} {(x)}^{3 - 0} \cdot {(\frac{1}{x})}^{0} + \frac{3!}{(3 - 1)! 1!} {(x)}^{3 - 1} \cdot {(\frac{1}{x})}^{1} + \frac{3!}{(3 - 2)! 2!} {(x)}^{3 - 2} \cdot {(\frac{1}{x})}^{2} + \frac{3!}{(3 - 3)! 3!} {(x)}^{3 - 3} \cdot {(\frac{1}{x})}^{3}$

Step 3

Simplify the exponents for each term of the expansion.

$1 \cdot {(x)}^{3} \cdot {(\frac{1}{x})}^{0} + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Step 4

Simplify each term.

Multiply ${(x)}^{3}$ by $1$ .

${(x)}^{3} \cdot {(\frac{1}{x})}^{0} + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Apply the product rule to $\frac{1}{x}$ .

$x^{3} \cdot \frac{1^{0}}{x^{0}} + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Anything raised to $0$ is $1$ .

$x^{3} \cdot \frac{1}{x^{0}} + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Anything raised to $0$ is $1$ .

$x^{3} \cdot \frac{1}{1} + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Divide $1$ by $1$ .

$x^{3} \cdot 1 + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Multiply $x^{3}$ by $1$ .

$x^{3} + 3 \cdot {(x)}^{2} \cdot {(\frac{1}{x})}^{1} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Simplify.

$x^{3} + 3 x^{2} \cdot \frac{1}{x} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Cancel the common factor of $x$ .

Factor $x$ out of $3 x^{2}$ .

$x^{3} + x (3 x) \cdot \frac{1}{x} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Cancel the common factor.

$x^{3} + x (3 x) \cdot \frac{1}{x} + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Rewrite the expression.

$x^{3} + 3 x + 3 \cdot {(x)}^{1} \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Simplify.

$x^{3} + 3 x + 3 \cdot x \cdot {(\frac{1}{x})}^{2} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Apply the product rule to $\frac{1}{x}$ .

$x^{3} + 3 x + 3 x \cdot \frac{1^{2}}{x^{2}} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

One to any power is one.

$x^{3} + 3 x + 3 x \cdot \frac{1}{x^{2}} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Cancel the common factor of $x$ .

Factor $x$ out of $3 x$ .

$x^{3} + 3 x + x \cdot 3 \cdot \frac{1}{x^{2}} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Factor $x$ out of $x^{2}$ .

$x^{3} + 3 x + x \cdot 3 \cdot \frac{1}{x \cdot x} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Cancel the common factor.

$x^{3} + 3 x + x \cdot 3 \cdot \frac{1}{x \cdot x} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Rewrite the expression.

$x^{3} + 3 x + 3 \cdot \frac{1}{x} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Combine $3$ and $\frac{1}{x}$ .

$x^{3} + 3 x + \frac{3}{x} + 1 \cdot {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Multiply ${(x)}^{0}$ by $1$ .

$x^{3} + 3 x + \frac{3}{x} + {(x)}^{0} \cdot {(\frac{1}{x})}^{3}$

Anything raised to $0$ is $1$ .

$x^{3} + 3 x + \frac{3}{x} + 1 \cdot {(\frac{1}{x})}^{3}$

Multiply ${(\frac{1}{x})}^{3}$ by $1$ .

$x^{3} + 3 x + \frac{3}{x} + {(\frac{1}{x})}^{3}$

Apply the product rule to $\frac{1}{x}$ .

$x^{3} + 3 x + \frac{3}{x} + \frac{1^{3}}{x^{3}}$

One to any power is one.

$x^{3} + 3 x + \frac{3}{x} + \frac{1}{x^{3}}$

Expand Using the Binomial Theorem (x+1/x)^3

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