Áp dụng hằng đẳng thức $(a+b)^3=a^3+3a^2b+3ab^2+b^3$
a) $-(3+2y)^3=-(3^3+3.3^2.2y+3.3.(2y)^2+(2y)^3$
$=-(27+54y+36y^2+8y^3)$
$=-27-54y-36y^2-8y^3$
b) $(a+2)^3=a^3+3.a^2.2+3.a.2^2+2^3$
$=a^3+6a^2+12a+8$
c) $(x+3y)^3=x^3+3.x^2.3y+3.x.(3y)^2+(3y)^3$
$=x^3.9x^2y+27xy^2+27y^3$