Simplify (a-9)(a+9)

$(a - 9) (a + 9)$

Step 1

Expand $(a - 9) (a + 9)$ using the FOIL Method.

Apply the distributive property.

$a (a + 9) - 9 (a + 9)$

Apply the distributive property.

$a \cdot a + a \cdot 9 - 9 (a + 9)$

Apply the distributive property.

$a \cdot a + a \cdot 9 - 9 a - 9 \cdot 9$

Step 2

Simplify terms.

Combine the opposite terms in $a \cdot a + a \cdot 9 - 9 a - 9 \cdot 9$ .

Reorder the factors in the terms $a \cdot 9$ and $- 9 a$ .

$a \cdot a + 9 a - 9 a - 9 \cdot 9$

Subtract $9 a$ from $9 a$ .

$a \cdot a + 0 - 9 \cdot 9$

Add $a \cdot a$ and $0$ .

$a \cdot a - 9 \cdot 9$

Simplify each term.

Multiply $a$ by $a$ .

$a^{2} - 9 \cdot 9$

Multiply $- 9$ by $9$ .

$a^{2} - 81$