d-b-b-a-a-c-b-b-d-d

`a, (5^2 +20:2^2):5`

`= (25 +20:4):5`

`= ( 25+5):5`

`= 30:5`

`= 6`

`b, (-1/4)^2 * (7/9) +1/16 * (-2/9)`

`= 1/16 * (7/9) +1/16 * (-2/9)`

`=1/16 * (7/9 + (-2)/9)`

`= 1/16* 5/9`

`= 5/144`

`c, 5/12 - (-1/4+ 5/12) : 7/6 -1`

`=5/12 - ( -3/12 +5/12) xx 6/7 -1`

`= 5/12 - 2/12 xx 6/7-1`

`=  5/12 - 1/6xx 6/7-1`

`= 5/12 - 6/42-1`

`= 5/12 - 1/7 -1`

`= 23/84-1`

`= -61/84`

`-(x-2y)(3xy+6x^2+x)`

`=-(3x^2 y + 6x^3 +x^2 -6xy^2 - 12x^2y -2xy)`

`=-( 6x^3 +x^2 -2xy-9x^2 y -6xy^2)`

`= -6x^3 -x^2 +2xy +9x^2y+6xy^2`

__

`-(18x^4y^3 -24x^3y^4 -12x^3y^3):(6x^2y^3)`

`= - ( 3x^2- 4xy - 2x)`

`= -3x^2+4xy+2x`

`x^2-2xy+y^2`

`=(x-y)^2`

Tại `x=11;y=1`

Ta có : `(x-y)^2 = (11-1)^2=10^2=100`

`3xy-9x^2`

`=3x(y-3x)`

`25-x^2+2xy-y^2`

`=25-(x^2-2xy+y^2)`

`= 25-(x-y)^2`

`=(5-x+y)(5+x+y)`

__

`x^3-3x^2-4x+12`

`=(x^3-3x^2)-(4x-12)`

`= x^2(x-3)-4(x-3)`

`=(x-3)(x^2-4)`

`=(x-3)(x-2)(x+2)`

`x^2-5x+6`

`=x^2-2x-3x+6`

`= x(x-2)-3(x-2)`

`=(x-2)(x-3)`

Là trường hợp âm (-) với dương (+) nha.

`x^2 -5x-14=0`

`<=>x^2 +2x-7x-14=0`

`<=> (x^2 +2x)-(7x+14)=0`

`<=> x (x+2)-7(x+2)=0`

`<=>(x+2)(x-7)=0`

\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\x-7=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-2\\x=7\end{matrix}\right.\)

`(x+2)^2 =64`

`=>(x+2)^2=(+-8)^2`

`@ TH1`

`x+2=8`

`=>x=8-2`

`=>x=6`

`@ TH2`

`x+2=-8`

`=>x=-8-2`

`=>x=-10`

số 12 ạ ⚡☕