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818jasmine
in a plane, if two lines are perpendicular to the same line, then they are what to each other.
Have you tried drawing a sketch? 1) Draw a line. 2) Make a second line perpendicular (90 degrees) to the first one. 3) Draw another line perpendicular to the very first line. How are lines 2 and 3 related? (parallel, perpendicular, intersecting at 45 degrees, etc?) Hope this helps.
You can also think about slope. if they are mutually perpendicular to a common line of arbitrary slope, how are their slopes related? (perpendicular lines have opposite reciprocal slopes)
they are parallel aren't they
if the common line has slope a, the two perpendiculars have slope -1/a. Since their slope is the same they are parallel
what are the exterior angles of a triangle is it 360 degrees