What is the projection of line
segment 𝐴𝐷 onto line 𝐴𝐶?
First of all, we want to know what
our target line is. This is the line on which our
projection will fall. Since we want to know the
projection of line segment 𝐴𝐷 onto line 𝐴𝐶, line 𝐴𝐶 is our target line. First, we identify line 𝐴𝐶, and
then we need the segment that we want to make a projection of, which is 𝐴𝐷. To visualize a projection, we need
to visualize a light source that is perpendicular to our target line. In this diagram, we already have a
line segment that’s perpendicular to our target line. That’s the line segment 𝐷𝑀. We’ll use lines that are parallel
to 𝐷𝑀 to find this projection.
If we want to know what kind of
shadow this line segment 𝐴𝐷 would create, it would fall between 𝐴 and 𝑀 on our
target line, with the line segment 𝐴𝑀 being its shadow. That shadow portion is the
projection. And so we say that the projection
of line segment 𝐴𝐷 onto line 𝐴𝐶 would be line segment 𝐴𝑀.