The triangle ABC in the plane has vertices A(1, 0), B(3, 1), C(2, 2). The triangle PQR has vertices P(−1, 0), Q(−3, 1), R(−2, 2). Draw a rough sketch of the two triangles, and by explicitly describing an isometry between them (or otherwise), show that the triangles ABC and PQR are congruent.

I've drawn the sketch, I just don't understand what to do for "by explicitly describing an isometry between them (or otherwise), show that the triangles ABC and PQR are congruent."

An isometry is the way you map a point on a figure to the corresponding point on a congruent figure. If your sketch is correct, you'll see that the two triangles are reflections of each other across the y-axis. So you can use that as the expicit description, or as a general rule (not just for veticies) *any* point (x,y) on firgure 1 maps such that \[(x,y)\rightarrow(-x,y)\] on figure 2.

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