Oliver is trying to solve the following equation by completing the square.
x2−32x+31=0
Here are the steps Oliver used to complete the square.

Original equation: Line 1: Line 2: Line 3: Line 4: Line 5: Line 6: x2−32x+31x2−32xx2−32x+32(x−16)2(x−16)2−−−−−−−−√x−16x=======0−31−31+3211–√±115 and x=17
Oliver did not get the correct solutions.

Which line contains Oliver's first mistake?