Viết khai triển theo nhị thức Newton: a) (x + y)6; b) (1 – 2x)5.

a) (x + y)⁶ =C60x6+C61x5y+C62x4y2+C63x3y3+C64x2y4+C65xy5+C66y6

=x6+C61x5y+C62x4y2+C63x3y3+C64x2y4+C65xy5+y6.

b) (1 – 2x)⁵ = [(–2x) + 1]⁵

= C50(–2x)⁵ + C51(–2x)⁴1 + C52(–2x)³1² + C53(–2x)²1³ + C54(–2x)1⁴ + C551⁵

= –2⁵x⁵ + C512⁴x⁴ – C522³x³ + C532²x¹ + C542x + 1.