Question

Answer 1

6)

a)(x-1)(x+2)=x²+2x-x-2=x²-x-2

b) (x-2)(x²+2x+4)=x³-8(HĐT số 7)

c)(x+y)(x-y)=x²-y²(HĐT số 3)

d)(x-2y)(x²+2xy+4y²)=x³-8y³(HĐT số 7)

 

 

Answer 2

7) 

(x-2)(x+3)-(x+1)(x-4)

=x²+3x-2x-6-(x²-4x+x-4)

= x²+3x-2x-6-x²+4x-x+4=4x-2

Answer 3

Bài 9:

Ta có: \(\left(x-y\right)\left(x^2+xy+y^2\right)-\left(x+y\right)\left(x^2-y^2\right)\)

\(=x^3-y^3-\left(x^3-xy^2+x^2y-y^3\right)\)

\(=x^3-y^3-x^3+xy^2-x^2y+y^3\)

\(=xy^2-x^2y\)

\(=xy\left(y-x\right)\)

\(=\left(-2\right)\cdot\left(-1\right)\cdot\left(-1+2\right)\)

=2