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Trick to draw an 80 degree angle accurately (file:- Draw10.htm)

This is a small "sidebar" to a page about drawing angles without a protractor.

It shows you how to draw an 80 degree angle by drawing a 10 degree angle from a "different base, and how to reliably, accurately, construct" that "different base".

Suppose you want to draw...


Start by "constructing" a perpendicular to the line. You can do this accurately as follows...

Using a compass, on one setting, mark a "B" and a "C", each the same distance from "A".


Then increase the radius the compass is set to, and (again keeping the new setting unchanged) draw two arcs...


The perpendicular rises from A, and passes through where the two arcs intersect.


Now use the technique on this page's parent page (or other) to draw a 10 degree angle, from AD. That will also be an 80 degree angle from AC.


Think about the geometries involved. If you are creating the angles by some techniques, the 10 degree angle can be drawn more accurately than the 80 degree angle can be drawn directly.

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