\[1)\ Сумма:\]
\[4x^{2} - 7x - 6 + 4x - 10x^{2} + 3 =\]
\[= - 6x^{2} - 3x - 3.\]
\[2)\ Разность:\]
\[4x^{2} - 7x - 6 - \left( 4x - 10x^{2} + 3 \right) =\]
\[= 4x^{2} - 7x - 6 - 4x + 10x^{2} - 3 =\]
\[= 14x^{2} - 11x - 9.\]