câu 1:
a , 5x(3x^2+5x-6)=15^3+25x^2-30x
b,3x^2 ( 4x^3 - 2x^2 + 7x)=12x^5-6x^4+21x^3
c,(3x + 1) . ( 5x^2 - 4)=3x.( 5x^2 - 4)+1. ( 5x^2 - 4)=15x^3-12x+5x^2-4
d,(7xy + 5x) . (2x^2y - 5xy + 4xy^2)= 7xy . (2x^2y - 5xy + 4xy^2) + 5x . (2x^2y - 5xy + 4xy^2)=14x^3y^2-35x^2y^2+27x^2y^3+10x^3y-25x^2y+20xy^2
câu 2:
b,27x^4y^5z^6 / 9x^4y^3z^2=3y^2z^4
c) ( x + y )^2 / ( x + y )= x + y
d) (x - y )^6 / (y-x)^5= x - y
câu 3:
a, 3x^2 - 6x = 0
<=>3x(x-2)=0
<=> 3x=0 hoặc x-2=0
<=>x=0 hoặc x=2
b,x^2-x=x(x-1)