<Dd> x = − b ± b 2 − 4 a c 2 a . (\ displaystyle x = (\ frac (- b \ pm (\ sqrt (b ^ (2) - 4ac))) (2a)).) </Dd> <P> This formula may not always produce an accurate result . For example, when c (\ displaystyle c) is very small, loss of significance can occur in either of the root calculations, depending on the sign of b (\ displaystyle b). </P> <P> The case a = 1 (\ displaystyle a = 1), b = 200 (\ displaystyle b = 200), c = − 0.000015 (\ displaystyle c = - 0.000015) will serve to illustrate the problem: </P> <Dl> <Dd> x 2 + 200 x − 0.000015 = 0 . (\ displaystyle x ^ (2) + 200x - 0.000015 = 0 .) </Dd> </Dl>

What is an exact number and how does it affect the number of significant figures in a calculation