b: \(2x^2-7xy+3y^2+x-3y\)

\(=2x^2-6xy-xy+3y^2+x-3y\)

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

\(=\left(x-3y\right)\left(2x-y+1\right)\)

Lời giải:
a.

Đặt $2a^2+5ab-3b^2-7b-2=(a+mb+n)(2a+pb+k)$ với $m,n,p,k$ nguyên 

$\Leftrightarrow 2a^2+5ab-3b^2-7b-2=2a^2+ab(2m+p)+mpb^2+a(k+2n)+b(km+np)+kn$ 

Đồng nhất hệ số:

\(\left\{\begin{matrix} 2m+p=5\\ mp=-3\\ k+2n=0\\ km+np=-7\\ kn=-2\end{matrix}\right.\)

Giải hpt này ta thu được $m=3; n=1; p=-1; k=-2$

Vậy $2a^2+5ab-3b^2-7b-2=(a+3b+1)(2a-b-2)$

b. Đa thức không phân tích được thành nhân tử

lm theo pp đồng nhất hệ số ạ

b: Ta có: \(2x^2-7xy+3y^2+x-3y\)

\(=2x^2-6xy-xy+3y^2+x-3y\)

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

\(=\left(x-3y\right)\left(2x-y+1\right)\)

\(X^2y+xy^2-x-y\)
\(=xy(x+y)-(x+y)=(xy-1)(x+y)\)

\(x^2y+xy^2-x-y=xy\left(x+y\right)-\left(x+y\right)=\left(x+y\right)\left(xy-1\right)\)

\(x^2y+xy^2-x-y=\left(x^2y+xy^2\right)-\left(x+y\right)=xy\left(x+y\right)-\left(x+y\right)=\left(xy-1\right)\left(x+y\right)\)

\(3x^2-3y^2-x+y\\ =3\left(x^2-y^2\right)-\left(x-y\right)\\ =3\left(x-y\right)\left(x+y\right)-\left(x-y\right)\\ =\left(x-y\right)\left[3\left(x+y\right)-1\right]\\ =\left(x-y\right)\left(3x+3y-1\right)\)

\(3x^2-3y^2-x+y=3\left(x^2-y^2\right)-\left(x-y\right)=3\left(x-y\right)\left(x+y\right)-\left(x-y\right)=\left(x-y\right)\left[3\left(x+y\right)-1\right]=\left(x-y\right)\left(3x+3y-1\right)\)

\(x^3+y^3+x+y\)

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

\(=\left(x+y\right)\left(x^2-xy+y^2+1\right)\)

3 x y 2 – 6 x 2 y = 3 x y (   y   –   2 x )

x 3   –   6 x 2 y   +   12 x y 2   –   8 y 3   =   x 3   –   3 . x 2 . ( 2 y )   +   3 . x . ( 2 y ) 2   –   ( 2 y ) 3     =   ( x   –   2 y ) 3

đáp án cần chọn là: D

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

\(x^3-6x^2y+12xy^2-8y^3=\left(x-2\right)^3\)

\(a,=xy\left(-6x+y\right)\)

\(b,=10c\left(a^2-9b^2+3bc-ac\right)=10c\left[\left(a-3b\right)\left(a+3b\right)-c\left(a-3b\right)\right]\)

\(=10c\left[\left(a-3b\right)\left(a+3b-c\right)\right]\)

c,\(=a\left(x-c\right)-b\left(x-c\right)=\left(a-b\right)\left(x-c\right)\)

d,\(=-\left(x-2y-6\right)\left(x-2y+6\right)\)

e;\(=m^2+4m+mn+n^2+4n+mn=m\left(m+4+n\right)+n\left(m+4+n\right)\)\(=\left(m+n\right)\left(m+n+4\right)\)

f,\(=\dfrac{1}{2}\left(4x^2-y^2\right)=\dfrac{1}{2}\left(2x-y\right)\left(2x+y\right)\)