Final answer:
The first error in the proof is in statement 3. The reason stated is not correct and should be 'segment addition' instead of 'addition property of equality.'
Step-by-step explanation:
The first error in this proof is in statement 3. The reason stated, 'addition property of equality,' does not justify the statement. Instead, the reason should be 'segment addition.'
To prove a line segment, you need to use the segment addition property, which states that if three points are collinear, the sum of the lengths of the two smaller segments is equal to the length of the larger segment. In this case, the correct reason to justify statement 3 would be 'segment addition.'