$\begin{cases} mx + y = -1\\x+y=-m\\\end{cases}$

 `<=>` $\begin{cases} -y=mx  +1\\-y = x+m\\\end{cases}$

`<=>`  $\begin{cases} y=-mx  -1\\y = -x-m\\\en ...

`2x - x^2 + sqrt(6x^2 - 12x + 7) = 0` 

`<=> -(x^2 - 2x) + sqrt(6(x^2 - 2x)+ 7) = 0`

Đặt `t = x^2 - 2x`  `(t >= -7/6)`

`<=> -t + sqrt(6t + 7) = ...

Ta có:
`2x-y=3`
`<=>2x-3=y`
`+)x=0`
`=>2.0-3=y`
`<=>y=-3`
`A(0;-3)`
`+)y=0`
`=>2x-3=0`
`<=>2x=3`
`<=>x={3}/{2} ...

Ta có:
`AB=3=>AB^2=3^2`
`AC=4=>AC^2=4^2`
`=>AB^2+AC^2=3^2+4^2=9+16=25`
Mà: `BC^2=25`
`=>AB^2+AC^2=BC^2`
Theo định lý pytago đảo < ...

`a,`
`n_{Al}={0,54}/{27}=0,02(mol)`
PTHH:
`4Al+3O_{2}->2Al_{2}O_{3}`
Theo PTHH ta có:
`n_{Al_{2}O_{3}}=0,02.{1}/{2}=0,01(mol)`
`m_{Al_{2}O_{3}}=0,01(54.2+16. ...

Với:
`a,b,c>=0` 
thì: `a+b+c>=3`$\sqrt[3]{abc}$ 

`a,`
`A=4x^2-4x+23`
`=(2x)^2-2.2x+1+22`
`=(2x+1)^2+22>=22`
Dấu "=" xảy ra khi:
`2x+1=0`
`<=>2x=-1`
`<=>x={-1}/{2}`
--------------------------- ...

Có: `y^2+2xy-3x-2=0`
`<=>y^2+2xy+x^2-x^2-3x-2=0`
`<=>(x+y)^2-x^2-2.x.{3}/{2}-{9}/{4}+{9}/{4}-2=0`
`<=>(x+y)^2-(x+3/2)^2+1/4=0`
`<=>(x+y)^2+(1/2-x- ...

Có:
`(a+b+c)^3+(a-b-c)^3+(b-c+a)^3+(c-a-b)^3`
`= a^3 + b^3 + c^3 + 3a^2b + 3ab^2 + 3a^2c + 3ac^2 + 3b^2c + 3bc^2 + 6abc+ a^3 - b^3 - c^3 - 3a^2b + 3ab^2 - 3a^2c + 3ac^2 + 3b^ ...

Có:
`(8x-3)(3x+2)-(4x+7)(x+4)=(2x+1)(5x-1)`
`<=>24x^2+16x-9x-6-4x^2-16x-7x-28-10x^2+2x-5x+1=0`
`<=>10x^2-19x-33=0`
Có:
`x = (-b ± √(b ...