Question

tim x biet 

x-8\(\sqrt{x}\)-9 =0

 

Answer 1

Đặt: \(\sqrt{x}=a\)

\(Taco:a^2-8a-9=0\Leftrightarrow a\left(a-8\right)-9=0\Leftrightarrow a\left(a-8\right)=9=1.9\)

\(\Leftrightarrow a=9\Leftrightarrow x=9^2=81\)

Answer 2

\(x-8\sqrt{x}-9=0\)

\(\Leftrightarrow\left(\sqrt{x}-9\right)\left(\sqrt{x}+1\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}\sqrt{x}=9\Leftrightarrow x=81\\\sqrt{x}=-1\left(loại\right)\end{cases}}\)

Vậy x = 81