Problem VI: To a given straight line AB and at a given point C in that line, to construct an angle given ACI equal to a given rectilineal angle E.
Construction: Construct above DE by the 4th problem, a perpendicular DF, meeting EF at F, and put at the point C in AB a line CG equal to ED, and from G construct over AB, by the preceding problem a perpendicular GH: I say that GI equals DF, and joining CI, the angle ACI will equal the angle E.
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Solution to Problem VII
The other eight problems
C. Edward Sandifer, "Van Schooten's Ruler Constructions - Solution to Problem VI," Convergence (August 2010)