<Dl> <Dd> x − r (\ displaystyle x-r) </Dd> </Dl> <Dd> x − r (\ displaystyle x-r) </Dd> <P> is a factor of the polynomial </P> <Dl> <Dd> a x 2 + b x + c (\ displaystyle ax ^ (2) + bx + c) </Dd> </Dl>

Chronological development of solution of a quadratic equation