a, 3x(x^3-2x)
=(3x*x^3)-(3x*2x)
=3x^4-6x^2
b, 4y^3/7x^2*14x^3/y
=4y^2*2x=8xy^2
c,x^2-9/2x+6*2,3-x=
=x^2-9/2x+6*2/3-x
=(x-3)(x+3)/2(x+3)*2/3-x
=-(x+3)/x+3
=-1
d, (2x/x-y)-(2y/x-y)
=2x-2y/x-y
=2(x-y)/x-y
=2
e, (x+15/x^2-9)+(2/x+3)
=(x+15/(x-3)*(x+3))+(2x-6/(x+3)*(x-3))
=x+15+2x-6/(x-3)*(x+3)
=3x+9/(x-3)*(x+3)
=3(x+3)/(x-3)*(x+3)
=3/x-3
CHÚC BN HỌC TỐT~~Hãy chọn mk nha
