\[x^{2} + (5x - 3)^{2} =\]
\[= x^{2} + (5x)^{2} - 2 \cdot 5x \cdot 3 + 3^{2} =\]
\[= x^{2} + 25x^{2} - 30x + 9 =\]
\[= 26x^{2} - 30x + 9.\]