There are given two parallel lines, a segment of length b, and a point A. Construct with compass and ruler a line that passes through A and intercepts the two parallel lines such as the segment of interception of the two parallel lines is of length b.

When A is between the two parallel lines I can construct a circle of diameter b and center A, but when A is not between them I dont know what to do. Please do not use the Intercept theorem as it should be solved only with compass and ruler


First construct one line that crosses the parallel lines at a distance of $b$.

Then construct a parallel to it through $A$.

  • $\begingroup$ Do you work for Staples? That was easy ;-) . +1 $\endgroup$ – Oscar Lanzi Nov 13 '16 at 10:39

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