In
Minimal area, we were asked to find the property of a line which minimized the area of the triangle it completed. It turned out the given point was the midpoint of the third side. In this problem, I am asking for a ruler and compass construction of that line, given the original angle and point.
See my solution for the "Minimal area"
problem for notation and solution.
If a = b, then construct the perpendicular
to the line VW through W.
If a = 90, then construct the perpendicular
to the line VW through W intersecting one
of the original rays at point B. Construct
point X on the other ray such that
|VX| = 2|WB|. Line XW is the desired line.
If a <> 90, then construct the perpendicular
to the line VW through W intersecting the
original rays at points A and B ( where
a = angle WVA). Construct
the circle passing through A, B, and V
intersecting ray VW again at U. Construct
point U' on line segment WB such that
|WU'| = |WU|. Construct point S on line
segment WA such that |AS| = |WB|. Construct
point T as the midpoint of line segment WS.
Construct point T' on line segment WV such
that |WT'| = |WT|. Construct the desired
line XY through W and parallel to line T'U'.
Proof of this construction.
|WU'| |WU|
tan(VWX) = tan(WT'U') = ------- = ------
|WT'| |WT|
|WA||WB| 2|WA||WB|
---------- -----------
|WV| |WV|
= ------------ = -------------
|WS|/2 |WA| - |WB|
|WA| |WB|
2 ------*------
|WV| |WV|
= -----------------
|WA| |WB|
------ - ------
|WV| |WV|
2 tan(WVX)*tan(WVY)
= ---------------------.
tan(WVX) - tan(WVY)
Edited on May 14, 2010, 6:09 pm
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Posted by Bractals
on 2010-05-13 12:55:53 |
Solution
