Question

[Trần Khánh Lan]

Bài 1 : Rút gọn
a) (a + b + c + d) (a - b -c - d)
b) (a - b - c - d) (a + b - c - d)
c) (a - b - c) ( a² + b² + c² + 2ab - ac - bc)
d) (a - b - c + d) (a + b - c - d)
e) (a - b - c) ( a² + b² + c² - 2ab + ac - bc)

Answer 1

[Trần Minh Hoàng]

a) (a + b + c + d)(a - b - c - d)

= a(a + b + c + d) - b(a + b + c + d) - c(a + b + c + d) - d(a + b + c + d)

= (aa + ab + ac + ad) - (ba + bb + bc + bd) - (ca + cb + cc + cd) - (da + db + dc + dd)

= aa - bb - cc - dd