(1)解:$x^2 - x - 6 = 0$
$(x - 3)(x + 2) = 0$
$x - 3 = 0$或$x + 2 = 0$
$x_1 = 3$,$x_2 = -2$
(2)解:$x^2 + 4x + 5 = 0$
$\Delta = 4^2 - 4×1×5 = 16 - 20 = -4 < 0$
方程無(wú)實(shí)數(shù)根
(3)解:$x^2 - 2x - 2 = 0$
$x^2 - 2x = 2$
$x^2 - 2x + 1 = 2 + 1$
$(x - 1)^2 = 3$
$x - 1 = ±\sqrt{3}$
$x_1 = 1 + \sqrt{3}$,$x_2 = 1 - \sqrt{3}$
(4)解:$p^2 + 5p - 1 = 0$
$p^2 + 5p = 1$
$p^2 + 5p + (\frac{5}{2})^2 = 1 + (\frac{5}{2})^2$
$(p + \frac{5}{2})^2 = \frac{29}{4}$
$p + \frac{5}{2} = ±\frac{\sqrt{29}}{2}$
$p_1 = \frac{-5 + \sqrt{29}}{2}$,$p_2 = \frac{-5 - \sqrt{29}}{2}$