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Dòng cuối bạn sửa lại giúp mình nhé. :(

\(\left(x-\dfrac{1}{3}\right)^2+\dfrac{3}{4}>0\forall x\)

a) `x^2+2x+2=(x^2+2x+1)+1=(x+1)^2+1 >0 forall x`

b) `x^2-x+1=[x^2 -2.x. 1/2 + (1/2)^2 ]+ 3/4`

`=(x^2-1/2)^2 + 3/4 >0 forall x`.

TH1: `3y-5=y+2`

`3y-y=2+5`

`2y=7`

`y=7/2`

TH2: `3y-5=-y-2`

`3y+y=-2+5`

`4y=3`

`y=3/4`

Vì x ở trong căn nên phải >=0 ạ

Vâng, x=20, mình tính sai. =)))))))

`1/8 xx 16^n =2^n`

`1/(2^3) xx (2^4)^n =2^n`

` 2^(-3) xx 2^(4n) =2^n`

` 2^(4n-3) =2^n`

`4n-3=n`

`3n=3`

`n=1` 

240km gấp 100km số lần là:

`240 : 100 = 2,4` (lần)

Đi 240km hết số lít xăng là:

`15 xx 2,4=36 (l)`

Đáp số:...

ĐK: `x>=0`.

`2\sqrt(20x)-2\sqrt(45x)+3/5 \sqrt(125x)=10`

`<=> 4\sqrt(5x) -6\sqrt(5x) +3\sqrt(5x)=10`

`<=>\sqrt(5x)=10`

`<=>5x=100`

`<=>x=25` (TM)

Vậy `S={25}`.