(2x + 3y)^2 = (2x + 3y)(2x + 3y)
= 2x(2x) + 2x(3y) + 3y(2x) + 3y(3y)
= 4x^2 + 6xy + 6xy + 9y^2
= 4x^2 + 12xy + 9y^2