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# How to Construct a Right-Angle

Preparation

## 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.

Your Drawing Instruments

Method One

## 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

(E) **Still keeping the set compass span**

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

(F) Placing your compass point at Point 3 and then Point 4,

###### draw the intersecting arcs c and d

(G) Join the arcs' intersection 5 to Point 1 with ruler and pencil

The angles AA and AB are both right angles

Method Two

## 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

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