Question

B6 ạ 

Answer 1

`b)C=8-6|x-7|-|y^2-1|`

Vì `|x-7| >= 0 AA x=>-6|x-7| <= 0 AA x`  và `-|y^2-1| <= y AA y`

   `=>-6|x-7|-|y^2-1| <= 0 AA x,y`

   `=>8-6|x-7|-|y^2-1| <= 8 AA x,y`

  Hay `C <= 8 AA x,y`

Dấu "`=`" xảy ra `<=>{(|x-7|=0),(|y^2-1|=0):}`

                           `<=>{(x-7=0<=>x=7),(y^2-1=0<=>y^2=1<=>y=+-1):}`

Answer 2

Bổ sung: bài `6(a)`

`A=3|2x-1|-1`

Vì `|2x-1| >= 0 AA x=>3|2x-1| >= 0 AA x`

   `=>3|2x-1|-1 >= -1 AA x`

  Hay `A >= -1 AA x`

Dấu "`=`" xảy ra `<=>|2x-1|=0<=>2x-1=0<=>x=1/2`

__________________________________________

`B=|x+1|+2(6,3-3y)^2+3`

Vì `|x+1| >= 0 AA x` và `2(6,3-3y)^2 >= 0 AA y`

  `=>|x+1|+2(6,3-3y)^2 >= 0 AA x,y`

  `=>|x+1|+2(6,3-3y)^2+3 >= 3 AA x,y`

    Hay `B >= 3 AA x,y`

Dấu "`=`" xảy ra `<=>{(|x+1|=0),((6,3-3y)^2=0):}`

                          `<=>{(x+1=0<=>x=-1),(6,3-3y=0<=>y=2,1):}`