(a-3b)^2+(a+3b)^2 = a^2 - 6ab + 9b^2 + a^2 + 6ab + 9b^2 = 2a^2 + 18b^2
(a+2)^2+(a-2)^2 = a^2 + 4a + 4 + a^2 - 4a + 4 = 2a^2 + 8
(x+3)^2-x(x+2) = x^2 + 6x + 9 - x^2 - 2x = 4x + 9
