3. 把下列方程化为$(x+m)^2=n(m, n$为常数$)$的形式.
(1)$x^2 - 3x = 2$；
(2)$x^2 - 2\sqrt{2}x - 4 = 0$；
(3)$a^2 - \frac{1}{9}a - 1 = 0$；
(4)$y^2 + y - 2 = 0$.

(1) $(x-\frac{3}{2})^2=\frac{17}{4}$
(2) $(x-\sqrt{2})^2=6$
(3) $(a-\frac{1}{18})^2=\frac{325}{324}$
(4) $(y+\frac{1}{2})^2=\frac{9}{4}$

4. 用配方法解下列方程.
(1)$4x^2 -25=0$；
(2)$9(2t-1)^2=36$；
(3)$x^2 -2x -5=0$；
(4)$x^2 -2\sqrt{3}x=5$；
(5)$3x^2 -x -1=0$；
(6)$\frac{1}{2}x^2 -x -3=0$；
(7)$-4x^2 +3x +1=0$.

(1) $x_1=\frac{5}{2}, x_2=-\frac{5}{2}$
(2) $t_1=-\frac{1}{2}, t_2=\frac{3}{2}$
(3) $x_1=\sqrt{6}+1, x_2=-\sqrt{6}+1$
(4) $x_1=2\sqrt{2}+\sqrt{3}, x_2=-2\sqrt{2}+\sqrt{3}$
(5) $x_1=\frac{1+\sqrt{13}}{6}, x_2=\frac{1-\sqrt{13}}{6}$
(6) $x_1=\sqrt{7}+1, x_2=-\sqrt{7}+1$
(7) $x_1=1, x_2=-\frac{1}{4}$