Some of the steps in the derivation of the quadratic formula are shown. step 4: step 5: step 6: step 7: which best explains why the expression cannot be rewritten as during the next step? negative values, like −4ac, do not have a square root. the ± symbol prevents the square root from being evaluated. the square root of terms separated by addition and subtraction cannot be calculated individually. the entire term b2 − 4ac must be divided by 2a before its square root can be determined.