# Difference of Perfect Squares

In this video, we are going to look at how to understand the difference of perfect squares.
For example:
When given something like $x^2-9$, we can rewrite it as
$x^2+0x-9$
To factor this, we will need two numbers that add up to 0 and multiply to -9. These numbers are 3 and -3. Therefore when we factor this, we will get
$(x+3)(x-3)$
Generally, whenever we have $x^2-b^2$ we will always be able to factor it as
$(x+b)(x-b)$
Or
$x^2-number$
will always be factored as
$(x+\sqrt{number})(x-\sqrt{number})$
For expressions more complex, such as
$4x^2-121y^4$
First, take the square root of the first term and place it in the front of each set of parentheses, and then take the square root of the second term and place it in the two parentheses with a plus or minus sign. This will be factored as
$(2x-11y^2)(2x+11y^2)$

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Used by students across the country. Pre-Algebra, Algebra I, Geometry, & Algebra II