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: A cube is sliced with a single straight cut, creating a two-dimensional cross-section. Name 2 different two-dimensional shapes that could result from the slice, and explain or draw how they are created.


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