Question

Justin is constructing a line through point Q that is perpendicular to line n. He has already constructed the arcs shown. A line n and an arc with center Q is drawn. Center Q lies above the line n. The arc cuts the line on two points A and B. A is left of B. Another arc is made with a center at A. The arc cut the line segment A B near point B. The arc is symmetric to line A B. He places his compass on point B to construct an arc. What must be true about the width of the compass opening when Justin draws the arc?

Answer 1

The compass must be the same width as it was when he constructed the arc from point A.

Explanation:

In order to construct a perpendicular line to a given line, we need to construct a point above and a point below the line such that the segment through them meets the line at a right angle.

When he constructed the arc from point A, it gave him one piece to creating these points. An arc from point B, intersecting the arc from point A at two points, will give him the two points he needs.

In order for the arc from point B to intersect the arc from point A, however, the width of the compass must be the same as it was when he constructed the arc from point A.

Answer 2

I believe that this problem has the following choices:

It must be equal to BQ .
It must be wider than when he constructed the arc centered at point A.
It must be equal to AB .
It must be the same as when he constructed the arc centered at point A.

The correct answer is the last one:

It must be the same as when he constructed the arc centered at point A.