standard_description: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.
problem_activity: Task
Plot the points (5,3), (-1,1), and (2,-3) in the coordinate plane and find the lengths of the three segments connecting the points.
Find the distance between (5,9) and (-4,2) without plotting the points.
If $(u,v)$ and $(s,t)$ are two distinct points in the plane, what is the distance between them? Explain how you know.
Does your answer to (c) agree with your calculations in parts (a) and (b)? Explain.


aligns: no