1: =>(5x-3)(5x+3)=0
=>x=3/5 hoặc x=-3/5
2: =>x2+8x+16-x2+1=16
=>8x+17=16
=>x=-1/8
1, \(25x^2-9=0\)
\(\Leftrightarrow25x^2=9\) \(\Leftrightarrow\left(5x\right)^2=3^2=\left(-3\right)^2\)\(\Leftrightarrow\left[{}\begin{matrix}5x=3\\5x=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{5}\\x=-\dfrac{3}{5}\end{matrix}\right.\)
2, \(\left(x+4\right)^2-\left(x+1\right)\left(x-1\right)=16\)
\(\Leftrightarrow\left(x+4\right)^2-\left(x^2-1\right)=16\)
\(\Leftrightarrow x^2+8x+16-x^2+1=16\)
\(\Leftrightarrow8x+17=16\Leftrightarrow8x=-1\Leftrightarrow x=-\dfrac{1}{8}\)
3, \(\left(2x-1\right)^2+\left(x+3\right)^2-5\left(x+7\right)\left(x-7\right)=0\)
\(\Leftrightarrow4x^2-4x+1+x^2+6x+9-5\left(x^2-49\right)=0\)
\(\Leftrightarrow5x^2+2x+10-5x^2+245=0\)
\(\Leftrightarrow2x+10+245=0\Leftrightarrow2x=-255\Leftrightarrow x=-\dfrac{255}{2}\)
