x2−9x+20=0x^{2}-9 x+20=0x2−9x+20=0
x2+9x+20=0x^{2}+9 x+20=0x2+9x+20=0
x2+9x−20=0x^{2}+9 x-20=0x2+9x−20=0
x2−9x−20=0x^{2}-9 x-20=0x2−9x−20=0