Video Transcript
Which of the following
represents the image of triangle 𝐴𝐵𝐶 after a reflection in the line 𝑀?
Remember, when we reflect a
single point, we preserve the perpendicular distance of this point from the
mirror line. This means we can reflect a
polygon by reflecting each of its vertices and then joining these together. Take, for instance, option
(A). If we reflect vertex 𝐵 in the
mirror line, we see that its image does not correspond to the image in the
second triangle. We have a similar issue with
the diagram in option (B).
However, when we reflect vertex
𝐵 in option (C), it corresponds to point 𝐵 prime in the second triangle. Reflecting point 𝐴 through the
mirror line corresponds to the point 𝐴 prime in the second triangle. And when we complete the same
process for point 𝐶, we do indeed see that this second triangle is a full
reflection through the mirror line. It’s worth noting that for
option (B) the triangle did look like it might be correct, but the vertices were
in the wrong order. So, we have confirmed that the
correct answer is option (C).
