Question

How do you factor the quadratic `x^2-121`?

Answer 1

`x^2-121=(x+11)(x-11)`

Explanation:

As `x^2` and `121=11^2` are both squares of `x` and `11` and there is minus sign between their squares,

we can use the identity `a^2-b^2=(a+b)(a-b)`

observe that factors of difference of squares `a^2` and `b^2` are sum of `a` and `b` and difference of `a` and `b`

and then factors are sum of `x` and `11` and difference of `x` and `11`

i.e. `x^2-121=(x+11)(x-11)`