The figure below shows triangle NRM with r2 = m2 + n2: Triangle NRM has legs m and n, and r is the length of its longest side.

Ben constructed a right triangle EFD with legs m and n, as shown below:

Triangle EFD has legs m and n and hypotenuse f.

He made the following table to prove that triangle NRM is a right triangle:

StatementReason
1. r2 = m2 + n2Given
2. f2 = m2 + n2?
3. f2 = r2Substitution
4. f = rSquare Root Property of Equality
5. Triangle NRM is congruent to triangle EFDSSS Postulate
6. Angle NRM is a right angleCPCTC
7. Triangle NRM is a right triangleAngle NRM is a right angle

Which reason best fits statement 2?
AAS postulate
Pythagorean Theorem
Triangle Proportionality Theorem
SSS postulate