=$a, 3x²-7x+2$
$=3x^2-6x-x+2$
$=3x(x-2)-(x-2)$
$=(3x-1)(x-2)$
$b, M=(\frac{1-x^3}{1-x}-x):(\frac{1-x^2}{1-x-x^2+x^3})$
$=(\frac{1-x^3-x(1-x)}{1-x}):(\frac{1-x^2}{(1-x)-x^2(1-x)})$
$=\frac{1-x^3-x+x^2}{1-x}:\frac{(1-x^2)}{(1-x^2)(1-x)}$
$=\frac{(1-x^3)-x(1-x)}{1-x}.\frac{1-x}{1}$
$=(1-x^3)-x(1-x)$
$=(1-x)(1+x+x^2)-x(1-x)$
$=(1+x+x^2-x)(1-x)$
$=(1+x^2)(1-x)$