The image of ΔABC after a reflection across Line E G is ΔA'B'C'. 2 triangles are shown. Line E G is the line of reflection. Line segment D D prime has a midpoint at point F. Line segment C C prime has a midpoint at point G. Points B and B prime share a point. Which triangle must be a right triangle and why? ΔA'B'C' is right because it is the image of ΔABC. ΔADC is right because AA' intersects AC at A. ΔBCC' is right because B lies of the line of reflection. ΔBGC is right because Line E G is perpendicular-to CC'.

  ΔBGC is right because Line E G is perpendicular-to CC'

Step-by-step explanation:

The midpoints of the segments joining a triangle vertex with its reflected image will lie on the line of reflection. The segment will be perpendicular to the line of reflection.

In this scenario, a triangle will be right if it has a leg that is part of the segment joining reflected points, and a leg on the line of reflection. ΔBGC is such a triangle.

  ΔBGC is right

Comment on the problem statement

Point D came out of nowhere. A diagram would be most helpful.

it's both, now can you answer my most recent question?