(1)
x^2+2xy+y^2
=(x+y)^2
=(2-√3+2+√3)^2
=4^2
=16
(2)
x^2-y^2
=(x+y)(x-y)
=(2-√3+2+√3)(2-√3-2-√3)
=4×(-2√3)
=-8√3