How do you factor completely a^2 - 1 - 4b^2 - 4b?

1 Answer
Dec 18, 2016

a^2-1-4b^2-4b = (a-2b-1)(a+2b+1)

Explanation:

The difference of squares identity can be written:

A^2-B^2 = (A-B)(A+B)

Use this with A=a and B=2b+1 as follows:

a^2-1-4b^2-4b = a^2-(4b^2+4b+1)

color(white)(a^2-1-4b^2-4b) = a^2-(2b+1)^2

color(white)(a^2-1-4b^2-4b) = (a-(2b+1))(a+(2b+1))

color(white)(a^2-1-4b^2-4b) = (a-2b-1)(a+2b+1)