Expand Using the Binomial Theorem (9x+y)^3

${(9 x + y)}^{3}$

Step 1

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

$\sum_{k = 0}^{3} \frac{3!}{(3 - k)! k!} \cdot {(9 x)}^{3 - k} \cdot {(y)}^{k}$

Step 2

Expand the summation.

$\frac{3!}{(3 - 0)! 0!} \cdot {(9 x)}^{3 - 0} \cdot {(y)}^{0} + \frac{3!}{(3 - 1)! 1!} \cdot {(9 x)}^{3 - 1} \cdot {(y)}^{1} + \frac{3!}{(3 - 2)! 2!} \cdot {(9 x)}^{3 - 2} \cdot {(y)}^{2} + \frac{3!}{(3 - 3)! 3!} \cdot {(9 x)}^{3 - 3} \cdot {(y)}^{3}$

Step 3

Simplify the exponents for each term of the expansion.

$1 \cdot {(9 x)}^{3} \cdot {(y)}^{0} + 3 \cdot {(9 x)}^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Step 4

Simplify each term.

Multiply ${(9 x)}^{3}$ by $1$ .

${(9 x)}^{3} \cdot {(y)}^{0} + 3 \cdot {(9 x)}^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Apply the product rule to $9 x$ .

$9^{3} x^{3} \cdot {(y)}^{0} + 3 \cdot {(9 x)}^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Raise $9$ to the power of $3$ .

$729 x^{3} \cdot {(y)}^{0} + 3 \cdot {(9 x)}^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Anything raised to $0$ is $1$ .

$729 x^{3} \cdot 1 + 3 \cdot {(9 x)}^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Multiply $729$ by $1$ .

$729 x^{3} + 3 \cdot {(9 x)}^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Apply the product rule to $9 x$ .

$729 x^{3} + 3 \cdot (9^{2} x^{2}) \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Raise $9$ to the power of $2$ .

$729 x^{3} + 3 \cdot (81 x^{2}) \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Multiply $81$ by $3$ .

$729 x^{3} + 243 x^{2} \cdot {(y)}^{1} + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Simplify.

$729 x^{3} + 243 x^{2} \cdot y + 3 \cdot {(9 x)}^{1} \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Simplify.

$729 x^{3} + 243 x^{2} y + 3 \cdot (9 x) \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Multiply $9$ by $3$ .

$729 x^{3} + 243 x^{2} y + 27 x \cdot {(y)}^{2} + 1 \cdot {(9 x)}^{0} \cdot {(y)}^{3}$

Multiply ${(9 x)}^{0}$ by $1$ .

$729 x^{3} + 243 x^{2} y + 27 x y^{2} + {(9 x)}^{0} \cdot {(y)}^{3}$

Apply the product rule to $9 x$ .

$729 x^{3} + 243 x^{2} y + 27 x y^{2} + 9^{0} x^{0} \cdot {(y)}^{3}$

Anything raised to $0$ is $1$ .

$729 x^{3} + 243 x^{2} y + 27 x y^{2} + 1 x^{0} \cdot {(y)}^{3}$

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

$729 x^{3} + 243 x^{2} y + 27 x y^{2} + x^{0} \cdot {(y)}^{3}$

Anything raised to $0$ is $1$ .

$729 x^{3} + 243 x^{2} y + 27 x y^{2} + 1 \cdot {(y)}^{3}$

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

$729 x^{3} + 243 x^{2} y + 27 x y^{2} + y^{3}$

Expand Using the Binomial Theorem (9x+y)^3

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