## Answer

$a^2-9b^2$

## Step-by-step explanation

Problem to solve:

$\left(a+3b\right)\left(a-3b\right)$

1

The sum of two terms multiplied by their difference is equal to the square of the first term minus the square of the second term. In other words: $(a+b)(a-b)=a^2-b^2$, where:

- The first term ($a$) is $a$.
- The second term ($b$) is $3b$.

$a^2-\left(3b\right)^2$

2

The power of a product is equal to the product of it's factors raised to the same power

$a^2-9b^2$

## Answer

$a^2-9b^2$