To reflect the triangle across the line, we have to draw rays from each vertex of the triangle that are perpendicular to the line of reflection. Open up the compass so that it is wider than the distance between the triangle's vertices and the line of reflection and draw two arcs.
Next, place the compass needle point where the first arcs intersect the line of reflection and draw two more pairs of intersecting arcs, like below.
By drawing a line from each vertex to the point of intersection of the two arcs, we have drawn perpendicular lines to the line of reflection.
Next, we have to measure the distance between the vertices and the line of reflection and measure the same distance on the perpendicular line on the opposite side of the line of reflection.
If we repeat this procedure for the rest of the vertices, we can draw the reflected triangle.
b Note that the preimage and image are congruent. Therefore, if we find the perimeter of one we know the perimeter of the other. To find the hypotenuse, we will substitute the length of the legs in the Pythagorean Theorem.
