x2-6x=-5
x2-6x+9=-5+9
（x-3）²=4
x-3=±2
x1=1
x2=5
y2+3y-2=0
y2+3y+2.25=2+2.25
（y+1.5）²=4.25
y+1.5=±0.5√17
y1=0.5√17-1.5
y2=-0.5√17-1.5
a2-6a=-1
a2-6a+9=-1+9
（a-3）²=8
a-2=±2√2
a1=2+2√2
a2=2-2√2
x2-4x+3=0
x2-4x+3+1=1
x2-4x+4=1
（x-2）²=1
x-2=±1
x1=1
x2=3
2y2+8y+7=0
y²+4y+3.5=0
y²+4y+3.5+0.5=0.5
y²+4y+4=0.5
(y+2)²=0.5
y+2=±√2/2
y1=√2/2 -2
y2=-√2/2 -2
- x2-3x=1
x2+3x=-1
x2+3x+2.25=-1+2.25
（x+1.5）²=1.25
x+1.5=±0.5√5
x1=√5 /2 -1.5
x2=-√5 /2 -1.5