8x²-1=（3x-1）（2x+3）
8x^2-1=6x^2+7x-3
2x^2-7x+2=0
x^2-7x/2=-1
(x-7/4)^2=33/16
x-7/4=土√33/4
x1=7/4+√33/4 x2=7/4-√33/4 .