\[(a + 1)x^{2} - 3ax + 4a = 0\]
\[D = 9a^{2} - 16a(a + 1) =\]
\[= a^{2} - 16a^{2} - 16a =\]
\[= - 7a^{2} - 16a\]
\[- 7a^{2} - 16a < 0\ \ \]
\[- a(7a + 16) = 0\]
\[a = 0,\ \ \ a = - \frac{16}{7} = - 2\frac{2}{7}\]