`= 1/9 - 27/64 - 64/27`

`= -179/576 -64/27`

`= (-179.3 - 64.64)/(1728)`

`=-4633/1728`

- Đề thiếu hã ?

a. `M=(x+2)/(x\sqrtx-1)+(\sqrt2+1)/(x+\sqrtx+1)-1/(\sqrtx-1)`

`=(x+2)/( (\sqrtx)^3 -1^3))+(\sqrt2+1)/(x+\sqrtx+1)-1/(\sqrtx-1)`

`= (x+2)/((\sqrtx-1)(x+\sqrtx+1)) + +(\sqrt2+1)/(x+\sqrtx+1)-1/(\sqrtx-1)`

`= ((x+2) +(\sqrt2+1)(\sqrtx-1)-(x+\sqrtx+1))/((\sqrtx-1)(x+\sqrtx+1))`

`=( \sqrt2 (\sqrtx-1))/((\sqrtx-1)(x+\sqrtx+1))`

`= (\sqrt2)/(x+\sqrtx+1)`

b. `x=9 => M=\sqrt2/(9+\sqrt9+1)=\sqrt2/13`

ĐK: `x \ne -1/2`

`| (x-7)/(2x+1)| >2`

`<=> ((x-7)^2)/((2x+1)^2) > 4`

`<=> ((x-7)^2-4(2x+1)^2)/((2x+1)^2)>0`

`<=> (-15x^2-30x+45)/((2x+1)^2) >0`

`<=> -15x^2-30x+45 > 0`

`<=> -15(x-1)(x+3)>0`

`<=> (x-1)(x+3) <0`

`<=> -3 <x<1`

Vậy `-3<x<1 ; x \ne -1/2`.

Ơ shao toàn lỗi tke nhỉ ._?

\(\left[{}\begin{matrix}2x+1=3x+5\\2x+1=-\left(3x+5\right)\end{matrix}\right.\)

\(\left[{}\begin{matrix}2x-1=-5x-2\\2x-1=-\left(5x-2\right)\end{matrix}\right.\)

`|x-2|>|3x+1|`

`<=> (x-2)^2 > (3x+1)^2`

`<=> x^2-4x+2>9x^2+6x+1`

`<=> -8x^2-10x+1>0`

`<=>(-5-\sqrt33)/8 < x < (-5+\sqrt33)/8`

`-(x-42,6+47,03): 27/4=0`

`-[x-(42,6-47,03)]=0`

`-(x+4,43)=0`

`x+4,43=0`

`x=-4,43`

Sửa: \(3km2hn=3000m+200m=3200m\)

`8/15 = 5/15+3/15=1/3+1/5`