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O is at the vertex of the angle, and either OX or OY along one arm. Then seen under<br />
which graduation the other arm of the angle lies. In the figure below, the angle AOC is<br />
50 0 .<br />
(c)Types of angles<br />
1. An angle of 90 0 is called a right angle. The lines that form a right angle are said<br />
to be perpendicular to each other.<br />
2. An angle less than a right angle is called an acute angle.<br />
3. An angle bigger than a right angle but less than 180 0 is called an obtuse angle.<br />
4. An angle bigger than 180 0 but less than 360 0 is called a reflex angles.<br />
(d) Drawing angles<br />
To make an angle of any given size at a point P in a line AB, place the protractor with<br />
the centre O at P, and the 0 0 – 180 0<br />
line of the protractor along AB. Make a very small dot at the edge of the protractor<br />
against the necessary graduation, at Q, say. Join QP.<br />
Exercise<br />
1 Using a ruler, draw on your paper a fairly large triangle and measure the number<br />
of degrees in each angle. Make a list of the sizes of the angles, and add them<br />
together.<br />
2 Draw the angle ABC which is 62 0 . Make AB = 5 cm long and<br />
BC = 6.5 cm long. Draw AC. How long is it?
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