Ta có:

\(3x-\frac{x^2}{x^2-9}=0\)

\(\Leftrightarrow3x=\frac{x^2}{x^2-9}\)

\(\Leftrightarrow3x\left(x^2-9\right)=x^2\)

\(\Leftrightarrow3x^3-27x^2=x^2\)

\(\Leftrightarrow3x^3=x^2+27x^2\)

\(\Leftrightarrow3x^3=28x^2\)

\(\Leftrightarrow3x=28\)

\(\Leftrightarrow x=\frac{28}{3}\)

Vậy \(x=\frac{28}{3}\)

Cậu ơi ! 

TH x = 0 thì sao ạ ?

Ta có \(3-\frac{8}{x^3}\)

\(=0=3-\frac{8}{x^3}=0=x=\frac{2}{^3\sqrt{3}}=y=\frac{9}{^3\sqrt{3}}=3^3\sqrt{9}\)

Vậy \(min\)của hàm số \(3x^2+\frac{4}{x}=3^3\sqrt{9}\)

Lê Tài Bảo Châu Không cần (a+b+c)² làm gì:) chỉ cần (a+b)² là OK r:))

\(5x^2+8xy+5y^2+4x-4y+8=0\)

\(\Leftrightarrow\left(x^2+4x+4\right)+\left(y^2-4y+4\right)+4\left(x^2+2xy+y^2\right)=0\)

\(\Leftrightarrow\left(x+2\right)^2+\left(y-2\right)^2+4\left(x+y\right)^2=0\)

\(VT=0\Leftrightarrow x=-2;y=2\)

Ai làm hướng dẫn mình cách làm nhanh ra hđt \(\left(a+b+c\right)^2\)ko tự nhiên bị ngu 

My favorite festival is Lunar New Year. On New Year's Day, everything seems so bustling, fun. I was given new clothes. Have a family reunion with the rice dish with delicious Tet holiday food. I get money lì xì. Great number of. On New Year's Day, the roads are so colorful. Peach blossom, apricot blossom, flowers bloom all the way. What a passionate New Year's Day! 
 

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