How to Construct a Right-Angle

What you Need

You will need:-

(a) Some Sheets of Plain A4 Paper
(b) A 25cm Ruler
(c) A 0.5mm Clutch Pencil

or
An Ordinary B-grade Pencil
A Block of Draftsman's Sandpaper

(d) A Pair of Good Quality Compasses

You may also want a:-

(e) Protractor

for checking your angles.

Bisection of a Semicircle

(A) Draw a line about 20mm from the long edge of a sheet of paper
(B) Use a compass point to make a small hole in the approximate center of the line ( Point 1 )



(C) Draw a semicircle about Point 1



(D) Without changing the compass span

Place the compass point at Intersection 2 and draw the arc a

Place the compass point at Intersection 3 and draw the arc b

draw the intersecting arcs c and d

An Angle Within a Semicircle

(A) Draw a line about 20mm from the long edge of a sheet of paper
(B) Use a compass point to make a small hole in the approximate center of the line ( Point 1 )



(C) Draw a semicircle about Point 1



(D) Draw a second line between Point 2 and any position on the semicircle



(E) Connect the Point 3 where the second line touches the semicircle with Point 4,
which is diametrically opposite Point 2




Angle AC is a right angle