Simplify (6-3i)(6+3i)

$(6 - 3 i) (6 + 3 i)$

Step 1

Expand $(6 - 3 i) (6 + 3 i)$ using the FOIL Method.

Apply the distributive property.

$6 (6 + 3 i) - 3 i (6 + 3 i)$

Apply the distributive property.

$6 \cdot 6 + 6 (3 i) - 3 i (6 + 3 i)$

Apply the distributive property.

$6 \cdot 6 + 6 (3 i) - 3 i \cdot 6 - 3 i (3 i)$

Step 2

Simplify and combine like terms.

Simplify each term.

Multiply $6$ by $6$ .

$36 + 6 (3 i) - 3 i \cdot 6 - 3 i (3 i)$

Multiply $3$ by $6$ .

$36 + 18 i - 3 i \cdot 6 - 3 i (3 i)$

Multiply $6$ by $- 3$ .

$36 + 18 i - 18 i - 3 i (3 i)$

Multiply $- 3 i (3 i)$ .

Multiply $3$ by $- 3$ .

$36 + 18 i - 18 i - 9 i i$

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

$36 + 18 i - 18 i - 9 (i^{1} i)$

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

$36 + 18 i - 18 i - 9 (i^{1} i^{1})$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$36 + 18 i - 18 i - 9 i^{1 + 1}$

Add $1$ and $1$ .

$36 + 18 i - 18 i - 9 i^{2}$

Rewrite $i^{2}$ as $- 1$ .

$36 + 18 i - 18 i - 9 \cdot - 1$

Multiply $- 9$ by $- 1$ .

$36 + 18 i - 18 i + 9$

Add $36$ and $9$ .

$45 + 18 i - 18 i$

Subtract $18 i$ from $18 i$ .

$45 + 0$

Add $45$ and $0$ .

$45$