Question

What is the product mentally of (ab + 3)(ab - 3)

Answer 1

`a^2b^2 - 9`

Explanation:

We are given the following expression and we are to determine its product mentally:

`( a b + 3 ) ( a b - 3 )`

For this, we can use the FOIL method, which stands for First, Outer, Inner, Last.

First means multiply the terms which come first in each of the binomial, Outer means multiply the outermost terms in the product. Inner means multiply the innermost two terms. Last means multiply the terms which occur last in each binomial.

So we get:

`ab*ab +3*(-3)=a^2b^2 - 9`

Answer 2

ab² - 9

Explanation:

Given in the question an expression

(ab + 3)(ab - 3)

To product mentally we will use polynomial identity called

Difference of squares

a² - b² = (a+b)(a-b)

here a = ab

b = 3

(ab + 3)(ab - 3) = ab² - 3² = ab² - 9