9x²+3x-1=0
D=b²-4ac
= 3²-4×9×-1
=9+36
=45
x1= (-b+VD)/2a
= (-3+V45)/2×9
= (-3+3V5)/18
=(-1+V5)/6
x2=(-b-VD)/2a
=(-3-3V5)/18
=(-1-V5)/6
