Question

x^2-225=0

Answer 1

Use:

\[\huge a^2 - b^2 = (a-b)(a+b)\]

Answer 2

You can write the above equation as:

\[\huge x^2 - 15^2 = 0\]

Now use that formula..

Answer 3

a^2 -b^2=0
(a+b)(a-b)=0
a=-b or a=b

x^2-225=0
x^2-(15^2)=0
(x-15)(x+15)=0
x-15=0 or x+15=0

the last step is left for you. :D