Because of the unique line postulate, we can draw unique line segment PM. Using the definition of reflection, PM can be reflected over line

"Consider the incomplete paragraph proof.

Given: P is a point on the perpendicular bisector, l, of MN.

Prove: PM = PN

The answer is point M. The easy way to think about it is well, we reflected PM, and it already says that ""point P is the image of itself"". What else was reflected aside from P? It's only point M.

You can also think that since we are using the property of reflections to preserve length, and PN is the reflected line segment, where did N come from? It wasn't P, because we retained point P. Then it must have come from the reflection of M.

When asked to complete proof, try your best to follow the proof's train of thought. Look at what happens after the blank, and try to work your way backwards.

Hope this helps somewhat!"