\[(1 - 5x)(1 + 5x) - (3x - 1)^{2} =\]
\[= 1 - (5x)^{2} - \left( (3x)^{2} - 2 \cdot 3x + 1 \right) =\]
\[= 1 - 25x^{2} - 9x^{2} + 6x - 1 =\]
\[= - 34x^{2} + 6x = 2x(3 - 17x).\]