Question

7. We learned that in a plane, two lines perpendicular to the same line are parallel. Use the rectangular solid below to explain why the words "in a plane" are needed.

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Answer 1

"In a plane" imposes the condition that these 3 lines exist in ONLY 2 dimensions, otherwise, the statement, "Two lines perpendicular to the same line are parallel" is false.

Example 1: lines CE & DF are // & perpendicular to CD. TRUE

Example 2: lines CE & BD are // & perpendicular to CD. FALSE

Explanation:

hope this helped :P