Question 176146
As in your instructions, the first think you should always look for is a GCF (greatest common factor).  In the problem here,
{{{9x^2-36y^2}}} what is the GCF?  Do 9 and 36 have anything in common?  Yes, because 36=9*4.  Do x^2 and y^2 have anything in common?  No.  So first, let's factor out a 9:
{{{9(x^2-4y^2)}}}
Ok, are we done, or can we factor some more?  Notice that both x^2 and 4y^2 are perfect squares.  This can be seen by writing the second term as (2y)^2.  So,
{{{9((x)^2-(2y)^2)}}}
now is in the format to factor it using difference of squares, which says that
{{{(a^2-b^2)=(a+b)(a-b)}}}
So, we have here that a=x and b=2y, so
{{{9(x+2y)(x-2y)}}}