1) -1/2x^2+x+2=0
x^2-2x-4=0
x^2-2x+1=5
(x-1)^2=5
x-1=根号5 或-根号5
x=1+根号5 或 x=1-根号5
2)x^2+x+2=0
x^2+x+1/4=-7/4
(x+1/2)^2=-7/4 (无解)
3)2x^2-8=0
x^2-4=0
(x+2)(x-2)=0
x1=-2 x2=2
4)(y-5)^2-36=0
(y-5)^2=36
y-5=6 或y-5=-6
y=11或y=-1