Bài 1: Rút gọn
a) A = (3x3 + 3x + 1)(3x3 - 3x + 1) - (3x3 + 1)2
b) B = (2x2 + 2x + 1)(2x2 - 2x + 1) - (2x2 + 1)2
Bài 2: CMR
a) (a2 + b2 - c2 )2 - (a2 - b2 + c2 )2 = 4ab2 - 4ac2
b) (a + b + c)2 + (a - b + c)2 + (a + b - c)2 + ( b + c - a)2 = 4(a2 + b2 + c)