Factor the expression 45x2 - 20y2.

The expression is $45x^2 - 20y^2$.

The coefficients are 45 and 20. The GCF of 45 and 20 is 5.
Factor out the GCF from the expression:

The expression inside the parentheses, $9x^2 - 4y^2$, is in the form $A^2 - B^2$.
Here, $A^2 = 9x^2$, so $A = \sqrt{9x^2} = 3x$.
And $B^2 = 4y^2$, so $B = \sqrt{4y^2} = 2y$.

The factored expression is: