# How do you solve #x^2 - 8x - 20 = 0# by completing the square?

##### 2 Answers

#### Explanation:

In addition to completing the square we can use the difference of squares identity:

#a^2-b^2 = (a-b)(a+b)#

with

#0 = x^2-8x-20#

#=(x-4)^2-4^2-20#

#=(x-4)^2-16-20#

#=(x-4)^2-36#

#=(x-4)^2-6^2#

#=((x-4)-6)((x-4)+6)#

#=(x-10)(x+2)#

So

#### Explanation:

This can be written as

Let

Add 16 to both sides:

We know that

Find the square root of both the sides:

When,

Add 4 to both sides:

When,

Add 4 to both sides: