Ta có :
\(49x^2-81=0\)
\(\Leftrightarrow\)\(\left(7x\right)^2-9^2=0\)
\(\Leftrightarrow\)\(\left(7x-9\right)\left(7x+9\right)=0\)
\(\Leftrightarrow\)\(\orbr{\begin{cases}7x-9=0\\7x+9=0\end{cases}\Leftrightarrow\orbr{\begin{cases}7x=0+9\\7x=0-9\end{cases}}}\)
\(\Leftrightarrow\)\(\orbr{\begin{cases}7x=9\\7=-9\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{9}{7}\\x=\frac{-9}{7}\end{cases}}}\)
Vậy \(x=\frac{9}{7}\) hoặc \(x=\frac{-9}{7}\)
Chúc bạn học tốt ~
\(49x^2-81=0\)
\(\Rightarrow\)\(\left(7x\right)^2=9^2\)
\(\Rightarrow\)\(7x=9\)
\(\Rightarrow\)\(x=\frac{9}{7}\)
\(49x^2-81=0\)
\(49x^2-9^2=0\)
\(\left(7x\right)^2-9^2=0\)
\(\left(7x-9\right)^2=0\)
\(7x-9=0\)
\(7x=9\)
\(x=\frac{9}{7}\)
Tk mk nhá
