\[5a + 3 - 2a^{2} + a + 7 =\]
\[= - 2a^{2} + 6a + 10.\]
\[5a + 3 - \left( - 2a^{2} + a + 7 \right) =\]
\[= 5a + 3 + 2a^{2} - a - 7 =\]
\[= 2a^{2} + 4a - 4.\]