`(x+2)-6(x-5) -10x=2`

`=> x+2 - (6x-30)-10x=2`

`=> x+2-6x+30-10x=2`

`=> (x-6x -10x) + (2+30)=2`

`=> -15x + 32 =2`

`=> -15x=2-32`

`=> -15x= -30`

`=>x=(-30)/(-15)`

`=>x=2`

13 - (-30) = 13 +30 = 43 á cậu - (- thành + nha.

\(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}\ge?\dfrac{1}{\sqrt{ab}}+\dfrac{1}{\sqrt{bc}}+\dfrac{1}{\sqrt{ca}}\\ \Leftrightarrow\dfrac{2}{a}+\dfrac{2}{b}+\dfrac{2}{c}\ge\dfrac{2}{\sqrt{ab}}+\dfrac{2}{\sqrt{bc}}+\dfrac{2}{\sqrt{ca}}\)

Áp dụng bất đẳng thức AM-GM ta có :

\(\dfrac{1}{a}+\dfrac{1}{b}\ge\dfrac{2}{\sqrt{ab}}\\ \dfrac{1}{b}+\dfrac{1}{c}\ge\dfrac{2}{\sqrt{bc}}\\ \dfrac{1}{c}+\dfrac{1}{a}\ge\dfrac{1}{\sqrt{ca}}\)

Vậy \(\dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}\ge\dfrac{1}{\sqrt{ab}}+\dfrac{1}{\sqrt{bc}}+\dfrac{1}{\sqrt{ca}}\left(đpcm\right)\)

`x-28 =8.(-5)`

`=> x-28= -40`

`=>x=-40+28`

`=>x=-12`

Vậy `x=-12`

`-(-x+13-142) +18=55`

`=> x - 13 +142=55-18`

`=> x - 13 +142=37`

`=> x-13=37-142`

`=>x-13=-105`

`=>x=-105+13`

`=>x=-92`

`a, 8xy^2-2x^2y`

`= 2xy ( 4y - x)`

`b, x(x-y) -y(y-x)`

`= x(x-y) + y(x-y)`

`= (x-y)(x+y)`

`c, x(x-1) + (1-x)^2`

`= x(x-1)+(x-1)^2`

`= (x-1) (x+x-1)`

`=(x-1)(2x-1)`