Rút gọn: a) x + (x + 4)(x - 4) - (x^2 + 1)(x^2 - 1); b) (y + 3)(y - 3)(y^2 + 9) - (y^2 + 2)(y^2 - 2); c) (a + b - c)^2 + (a - b)^2 - ab + 2bc

Bài 1: Rút gọn
a) x + (x + 4)(x - 4) - (x^2 + 1)(x^2 - 1)
b) (y + 3)(y - 3)(y^2 + 9) - (y^2 + 2)(y^2 - 2)
c) (a + b - c)^2 + (a - b)^2 - ab + 2bc
d) (a + b + c)^2 + (b + c - a)^2 + (c + a - b)^2 + (a + b - c)^2
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