Question

Giải phương trình : 

\(x^2-7x+8\)

Answer 1

\(x^2-7x+8=0\)

\(\Leftrightarrow\)\(x^2-2.\frac{7}{2}x+\frac{49}{4}-\frac{17}{4}=0\)

\(\Leftrightarrow\)\(\left(x-\frac{7}{2}\right)^2-\frac{17}{4}=0\)

\(\Leftrightarrow\)\(\left(x-\frac{7}{2}-\frac{\sqrt{17}}{2}\right)\left(x-\frac{7}{2}+\frac{\sqrt{17}}{2}\right)=0\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x-\frac{7}{2}-\frac{\sqrt{17}}{2}=0\\x-\frac{7}{2}+\frac{\sqrt{17}}{2}=0\end{cases}}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=\frac{7+\sqrt{17}}{2}\\x=\frac{7-\sqrt{17}}{2}\end{cases}}\)

Vậy....