Rút gọn: a) (x + y)^2 - (x - y)^2; b) 9^8 - (18^4 - 1)(18^4 + 1)

Rut gon.
a,(x+y)^2-(x-y)^2.
b,9^8-(18^4-1)(18^4+1)

a,(2x-y)(4x^2-2xy+y^2)
b,(6x^5y^2-9x^4y^3+15x^3y^4):3x^3y^2
c,(2x^3-21x^2+67x-60):(x-5).
d,(x^4+2x^3+x-25):(x^2+5).
e,(27x^3-8):(6x+9x^2+4)