standard_description: Prove theorems about triangles. Theorems include: measures of interior angles of a triangle sum to 180°; base angles of isosceles triangles are congruent; the segment joining midpoints of two sides of a triangle is parallel to the third side and half the length; the medians of a triangle meet at a point.
problem_activity: Task
Is the quadrilateral with vertices  $(-6, 2)$, $(-3,6)$, $(9, -3)$, $(6,-7)$
a rectangle? Explain.


aligns: no