(x – 2y + 3)2 + (x + 2y – 3)2
= [(x)2 + (- 2y)2 + (3)2 + 2 (x) (- 2y) + 2 (- 2y) (3) + 2 (x) (3)] + [(x)2 + (2y)2 + (- 3)2 + 2 (x) (2y) + 2 (2y) (- 3) + 2 (x) (- 3)]
… [(a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ac]
= x2 + 4y2 + 9 – 4xy – 12y + 6x + x2 + 4y2 + 9 + 4xy – 12y – 6x
= x + x2 + 4y2 + 4y2 + 9 + 9 – 4xy + 4xy – 12y – 12y + 6x – 6x
= 2x2 + 8y2 + 18 – 24y
