The root formula is x 1=(-b-√△)/(2a), and x2=(-b+√△)/(2a).

x 1-x2 = x 1 =(-b-√△+ b-√△)/(2a)=(-2 √△)/(2a)=-√△/ a

So | x1-x2 | = |-√△/a | = √△/| a | (√△ is the arithmetic square root, which is not negative, so the sign of absolute value is not needed).