x2−3x+7=0x^{2}-3 x+7=0x2−3x+7=0
x2−3x−7=0x^{2}-3 x-7=0x2−3x−7=0
9x2−27x+20=09 x^{2}-27 x+20=09x2−27x+20=0
9x2−27x−20=09 x^{2}-27 x-20=09x2−27x−20=0