3x²+2x-7=0
x²+2x/3=7/3
x²+2x/3+(1/3)²=7/3+1/9
(x-1/3)²=8/9
x-1/3=±(2√2)/3
x=(1±2√2)/3
-4x²-8x+1=0
x²+2x=1/4
x²+2x+1=1+1/4
(x+1)=5/4
x+1=±(√5)/2
x=-1±(√5)/2
x²+2mx-n²=0
x²+2mx=n²
x²+2mx+m²=m²+n²
(x+m)²=m²+n²
x+m=±√(m²+n²)
x=-m±√(m²+n²)
x²-2mx-m²=0（m＞0)
x²-2mx=m²
x²-2mx+m²=2m²
(x-m)²=2m²
x-m=±m√2
x=m±m√2