a) MTC: $12x^3y^3$
$\Rightarrow \frac{x}{4x^2y^3}=\frac{6x}{12x^3y^3}$
$\Rightarrow \frac{5}{6x^3y}=\frac{5.2.y^2}{12x^3y^3}=\frac{10y^2}{12x^3y^3}$
b)Ta có:
$6-2x=-2(x-3)$
$x^2-9=x^2-3^2=(x-3)(x+3)$
Mẫu thức chung: -2(x-3)(x+3)
$\Rightarrow \frac{5}{6-2x}=\frac{5}{-2\left(x-3\right)}=\frac{5\left(x+3\right)}{-2\left(x-3\right)\left(x+3\right)}$
$\Rightarrow \frac{3}{x^2-9}=\frac{3}{\left(x-3\right)\left(x+3\right)}=\frac{-2.3}{-2\left(x-3\right)\left(x+3\right)}=\frac{-6}{-2\left(x-3\right)\left(x+3\right)}$
c)Ta có :
$x^2+2xy=x(x+2y)$
$xy+2y^2=y(x+2y)$
$\Rightarrow $ MTC= $xy(x+2y)$
$\Rightarrow \frac{2}{x^2+2xy}=\frac{2}{x\left(x+2y\right)}=\frac{2y}{xy\left(x+2y\right)}$
$\Rightarrow \frac{1}{xy+2y^2}=\frac{1}{y\left(x+2y\right)}=\frac{x}{xy\left(x+2y\right)}$
