theorem :: QUIN_1:15

for x, a, b, c being Real st a <> 0 & delta (a,b,c) >= 0 & ((a * (x ^2)) + (b * x)) + c = 0 & not x = ((- b) - (sqrt (delta (a,b,c)))) / (2 * a) holds
x = ((- b) + (sqrt (delta (a,b,c)))) / (2 * a)