`A = 2x`
`B = y`
Now the question will look like;
Now multiply first bold part in bracket 1 which is A with the other bracket in italic which is (A-B). Then do the same for B in the first bracket and add the two.
`= A^2-AB+AB-B^2` notice that AB term cancels.
So we got;
(A+B)(A-B) = A^2-B^2
Put the real values of A and B;
`(A+B)(A-B) = A^2-B^2`
`(2x+y)(2x-y) = (2x)^2-y^2`
`(2x+y)(2x-y) = 4x^2-y^2`
So the answer is ` (2x+y)(2x-y) = 4x^2-y^2`