( 2x - 1 )2 + ( x + 3 )2 - 5( x + 7 )( x - 7 ) = 0
<=> ( 2x - 1 )2 + ( x + 3 )2 - 5( x2 - 72 ) = 0
<=> 4x2 - 4x + 1 + x2 + 6x + 9 - 5x2 + 245 = 0
<=> 2x + 255 = 0
<=> 2x = -255
<=> x = -255/2
\(pt< =>4x^2-4x+1+x^2+6x+9-5x^2+5.49=0\)
\(< =>2x+255=0< =>x=-\frac{255}{2}\)
\(\left(2x-1\right)^2+\left(x+3\right)^2-5\left(x+7\right)\left(x-7\right)=0\)
\(\Leftrightarrow\left(4x^2-4x+1\right)+\left(x^2+6x+9\right)-5\left(x^2-49\right)=0\)
\(\Leftrightarrow4x^2-4x+1+x^2+6x+9-5x^2+245=0\)
\(\Leftrightarrow2x+255=0\)
\(\Leftrightarrow2x=-255\)
\(\Leftrightarrow x=\frac{-255}{2}\)
Vậy tập nghiệm của phương trình là: \(S=\left\{\frac{-255}{2}\right\}\)