standard_description: Prove the slope criteria for parallel and perpendicular lines and use them to solve geometric problems (e.g., find the equation of a line parallel or perpendicular to a given line that passes through a given point).
problem_activity: Task
Is the quadrilateral with vertices  $(-6, 2)$, $(-3,6)$, $(9, -3)$, $(6,-7)$
a rectangle? Explain.


aligns: yes