Lesson 4 of 17
A parallel through a point
Show on a big screenCheck the gap between two window bars. It is the same at the top and the bottom.
Step 1 of 5
- The first line, and a point P above it.
- Rule a slanted line from P down to the first line, at Q.
- Strike an arc at Q. It leaves two marks.
- Copy that corner at P. Rule the new line through P.
- Measure square across (at 90° to the lines) at two places. The gaps match.
Copy the corner, carry the line
Rule a slanted line from P to the first line. Call the crossing Q. Copy the corner at Q onto the slanted line at P. The new arm points the same way as the first line.
Equal matching corners make the two lines parallel. Parallel lines keep the same gap.
Watch out!
Not meeting on your page does not prove parallel. Measure square across at two places.
Slip the compass. Watch the two gaps.
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Try the lab to finish this lesson.