\(\sqrt{4}.\sqrt{36}=2.6=12\)

e.\(MCNN:x\left(x-3\right)\left(x+3\right)\left(x-2\right)\)

\(\dfrac{2x+6}{x^3-9x}=\dfrac{2\left(x+3\right)}{x\left(x^2-9\right)}=\dfrac{2\left(x+3\right)\left(x-2\right)}{x\left(x+3\right)\left(x-3\right)\left(x-2\right)}\)

\(\dfrac{1}{x^2-5x+6}=\dfrac{1}{\left(x-2\right)\left(x-3\right)}=\dfrac{x\left(x+3\right)}{x\left(x+3\right)\left(x-3\right)\left(x-2\right)}\)

d.\(MCNN:3\left(x+2\right)^2\)

\(\dfrac{x+5}{x^2+4x+4}=\dfrac{3\left(x+5\right)}{3\left(x+2\right)^2}\)

\(\dfrac{x}{3x+6}=\dfrac{x\left(x+2\right)}{3\left(x+2\right)^2}\)

\(c.MCNN:3x\left(x-4\right)^2\)

\(\dfrac{2x}{x^2-8x+16}=\dfrac{2x.3x}{3x.\left(x-4\right)^2}=\dfrac{6x^2}{3x\left(x-4\right)^2}\)

\(\dfrac{x}{3x^2-12x}=\dfrac{x}{3x\left(x-4\right)}=\dfrac{x\left(x-4\right)}{3x\left(x-4\right)^2}\)

b) \(MCNN:x\left(x-2\right)\left(x+2\right)\)

\(\dfrac{1}{x+2}=\dfrac{x\left(x-2\right)}{x\left(x+2\right)\left(x-2\right)}\)

\(\dfrac{8}{2x-x^2}=\dfrac{8\left(x+2\right)}{x\left(x+2\right)\left(2-x\right)}=-\dfrac{8\left(x+2\right)}{x\left(x+2\right)\left(x-2\right)}\)

a)MCNN : 2(x+2)(x-2)

 \(\dfrac{3x}{2x+4}=\dfrac{3x}{2\left(x+2\right)}=\dfrac{3x\left(x-2\right)}{2\left(x-2\right)\left(x+2\right)};\dfrac{x+3}{x^2-4}=\dfrac{2\left(x+3\right)}{2\left(x-2\right)\left(x+2\right)}\)

CuO + HCl -> CuCl2 + H2O

nhân 2 vào trước HCl

CuO + 2HCl -> CuCl2 + H2O

a) = \(\left(\dfrac{x\left(x+y\right)-2x^2}{\left(x+y\right)}\right).\left(\dfrac{x-y+2y}{y\left(x-y\right)}\right)\)

\(=\dfrac{-x^2+xy}{x+y}.\dfrac{x+y}{xy-y^2}=\dfrac{xy-x^2}{xy-y^2}=\dfrac{x\left(y-x\right)}{-y\left(y-x\right)}=-\dfrac{x}{y}\)

Magie + Oxi -> Magie Oxit

Mg + O\(_2\) -> MgO

nhân số 2 trước MgO :

Mg + O\(_2->2MgO\)

nhân số 2 trước Mg

2Mg + O\(_2->2MgO\)