Find the product: (2x^2-9y)(2x^2+9y)

F= 2x^2 * 2x^2=4x^4
O= 2x^2 *9y=18x^2y
I= -9y*2x^2=-18yx^2
L= -9y*9y=-81y^2
4x^4+18x^2y-18yx^2-81y^2
4x^4-81y^2

Is this right?

Question

Find the product: (2x^2-9y)(2x^2+9y)

F= 2x^2 * 2x^2=4x^4
O= 2x^2 *9y=18x^2y
I= -9y*2x^2=-18yx^2
L= -9y*9y=-81y^2
4x^4+18x^2y-18yx^2-81y^2
4x^4-81y^2

Is this right?

anonymous · Answer

The answer is right (difference of 2 squares).

anonymous · Answer

Yes, I couldn't get through that equation, could you show me how to get through that one too. so far I have.

(a-b)^2=a^2 -2ab+b^2
(2x^2-9y)^2
=(2x^2)^2 -2(2x^2)(9y)+(9y)^2
2x^4-4x^2(9y)+9y^2

From there I dont know what to do. Do I *-4x^2 *9y?

anonymous · Answer

Square of A  - Square of B  is not the same as (A -B)^2.

Your 4x^4-81y^2 is the first one and factors (A+B)(A-B).

anonymous · Answer

The answer given in the original post is correct. $$4x^4-81y^2$$