Giúp em bt4,5 vs ạaaa c.on nhiều ạ

Bài `4` :

`A = x^2-4x-5`

`=(x^2-4x+4) - 9`

`= ( x-2)^2 - 9 >= -9`

`=> A >= -9`

Dấu ''='' `<=> x - 2 = 0 <=>x=2`

Vậy `min (A) = -9 <=>x=2`

`B = x^2-x-4`

`=(x^2-x+1/4) -17/4`

`= ( x-1/2)^2 - 17/4 <= -17/4`

`=> B <= -17/4`

Dấu ''='' `<=> x - 1/2 = 0 <=>x=1/2`

Vậy `min ( B ) = -17/4 <=>x=1/2`

Bài `5`:

`a)` `x^2-4x+4`

`=(x-2)^2`

`=(102-2)^2`

`=100^2`

`=10000`

`b)` `x^3+3x^2+3x+1`

`=(x+1)^3`

`= (999+1)^3`

`= 1000^3`

`= 1000 000 000`

Bài `4`

`A=x^2-4x-5`

`=x^2-4x+4-9`

`=(x-2)^2-9>=-9AAx`

Dấu "=" xảy ra khi `x-2=-9<=>x=-7`

Vậy `A_(min)=-9<=>x=-7.`$\\$

`B=x^2+x-4`

`=x^2+x+1/4-17/4`

`=(x+1/2)^2-17/4>=-17/4AAx`

Dấu "=" xảy ra khi `x+1/2=0<=>x=-1/2`

Vậy `B_(min)=-17/4<=>x=-1/2.`$\\$

Bài `5`

`a)` `x^2-4x+4`

`=(x-2)^2`

`=(102-2)^2`

`=100^2`

`=10  000`$\\$

`b)` `x^3+3x^3+3x+1`

`=(x+1)^3`

`=(999+1)^3`

`=1000^3`

`=1  000  000  000`