Đáp án:
Giải thích các bước giải:
a) x.(x-5)-4x+20 b) x.(x+6)-7x-42 c) x^2-2xy+y^2-xz+yz
=x.(x-5)-4x+4.5 =x.(x-6)-(7x+6.7) =(x^2-2xy+y^2)-(xz-yz)
=x.(x-5)-(4x-4.5) =x.(x+6)-7.(6+x) =(x-y)^2-z.(x-y)
=x.(x-5)-4.(x-5) =(6+x).(x-7) =(x-y).(x-y-z)
=(x-5).(x-4)
d) x^2-y^2-x+y e) a^3.x-ab+b-x
=(x^2-x)-(y^2-y) =(a^3.x-x)-(ab-b)
=x.(x-1)-y.(y-2) =x.(a^3-1)-b.(a-1)
=(a-1). (a-b)+a^2
