Expanding each expression:

(x+2)^2 = x^2 + 4x + 4

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

(5a+b)^2 = 25a^2 + 10ab + b^2

(a^2+b^2)^2 = a^4 + 2a^2b^2 + b^4