49x2 - 4 = 0
<=> (7x)2 - 22 = 0
<=> (7x - 2)(7x + 2) = 0
<=> \(\left[{}\begin{matrix}7x-2=0\\7x+2=0\end{matrix}\right.\)
<=> \(\left[{}\begin{matrix}x=\dfrac{2}{7}\\x=-\dfrac{2}{7}\end{matrix}\right.\)
\(49x^2-4=0\)
\(\Rightarrow49x^2=4\)
\(\Rightarrow x^2=\dfrac{4}{49}\)
\(\Rightarrow\left[{}\begin{matrix}x=\dfrac{2}{7}\\x=-\dfrac{2}{7}\end{matrix}\right.\)
49x2- 4=0
(7x)2 -22 = 0
(7x - 2).(7x + 2) = 0
7x-2 = 0 hay 7x + 2 = 0
x = 2/7 hay x = -2/7
vậy S= ( 2/7,-2/7)