Expand Using the Binomial Theorem (ax+by)^3

${(a x + b y)}^{3}$

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

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

Expand the summation.

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

Simplify the exponents for each term of the expansion.

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

Simplify each term.

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

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

Apply the product rule to $a x$ .

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

Apply the product rule to $b y$ .

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

Anything raised to $0$ is $1$ .

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

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

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

Anything raised to $0$ is $1$ .

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

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

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

Apply the product rule to $a x$ .

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

Simplify.

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

Simplify.

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

Apply the product rule to $b y$ .

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

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

$a^{3} x^{3} + 3 a^{2} x^{2} b y + 3 a x b^{2} y^{2} + {(a x)}^{0} \cdot {(b y)}^{3}$

Apply the product rule to $a x$ .

$a^{3} x^{3} + 3 a^{2} x^{2} b y + 3 a x b^{2} y^{2} + a^{0} x^{0} \cdot {(b y)}^{3}$

Anything raised to $0$ is $1$ .

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

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

$a^{3} x^{3} + 3 a^{2} x^{2} b y + 3 a x b^{2} y^{2} + x^{0} \cdot {(b y)}^{3}$

Anything raised to $0$ is $1$ .

$a^{3} x^{3} + 3 a^{2} x^{2} b y + 3 a x b^{2} y^{2} + 1 \cdot {(b y)}^{3}$

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

$a^{3} x^{3} + 3 a^{2} x^{2} b y + 3 a x b^{2} y^{2} + {(b y)}^{3}$

Apply the product rule to $b y$ .

$a^{3} x^{3} + 3 a^{2} x^{2} b y + 3 a x b^{2} y^{2} + b^{3} y^{3}$

Expand Using the Binomial Theorem (ax+by)^3

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