x²-2x=5
x²-2x+1=5+1
(x-1)²=6
x-1=±√6
x1=1+√6 x2=1-√6
（x+1）（x-1）+2（x+3）=8
x²-1+2x+6=8
x²+2x-3=0
(x+3)(x-1)=0
x1=-3 x2=1
1/2x²-x-3/2=0
x²-2x-3=0
(x+1)(x-3)=0
x1=-1 x2=3
x²-x-1=0
x²-x+(1/2)²=1+1/4
(x-1/2)²=5/4
x-1/2=±√5/2
x1=(1+√5)/2 x2=(1-√5)/2
x²-（2倍根号3+1）x+2倍根号3=0
(x-1)(x-2√3)=0
x1=1 x2=2√3