FIRST TERM
SUBJECT: BASIC TECHNOLOGY
CLASS: JSS 2
REFERENCE MATERIALS
- MELROSE, Basic Science and Technology, Book 2
- NERDC, Basic Technology for JSS, Book 2
WEEK SIX AND SEVEN
TOPIC: ANGLES
CONTENT
DEFINITION OF ANGLES
TYPES OF ANGLES
BISECTION AND CONSTRUCTION OF ANGLES.
ANGLES
An angle is formed when two straight lines intersect or meet at a point.
The sum of angle at the centre of a complete circle is 3600.
TYPES OF ANGLES
- Acute angles: - These are angles that are less than 900.
- Right angle: - This is an angle that is equal to 900.
- Obtuse angles: - These are angles that are greater than 900 but less than 1800.
- Reflex angles: - These are angles that are greater than 1800 but less than 3600.
- Complementary angles: - These are angles that sum up to 900.
- Supplementary angles: - These are angles that sum up to 1800.
EVALUATION
- Define an angle.
- Mention five types of angle and describe them.
CONSTRUCTION OF ANGLES
The following are several ways of constructing or drawing angles:
- Using a setsquare
- Using a combination of setsquares
- Using a protractor
- Using a pair of compasses
HOW TO CONSTRUCT ANGLES USING SETSQUARE
Standard angles are angles 300,450, 600 and 900. These angles can be drawn by simply using a setsquare. The method is simply choosing the appropriate setsquare that has the angle that is to be drawn. Thus 300-600 setsquare is used to draw 300, 600 and 900. Similarly, the 45-45 setsquare is used to draw 450 and 900.
EVALUATION
With the aid of a set square construct the following angle: i)900 ii) 600 iii)450
COMBINATION OF SETSQUARES
Setsquares can be combined to construct the following angles:
- To construct 750, combine 450 and 600 setsquares
1800- (600 + 450)= 750
- To construct 1350, combine 450 and 900
450+ 900 = 1350
- To construct 1050, combine 600 and 450
450+ 600 = 1350
EVALUATION
- Combine the sets-square to construct angles750 and 1350.
- Construct angle 60o
HOW TO DRAW AN ANGLE USING A PROTRACTOR
Procedure
- Place the protractor on the line from which the angle is to be formed. The baseline marked O at one end and, 180 marked at the other end.
- Set the centre of the protractor to start from where the vertex of the angle will be.
- Mark the required degree of the angles to be drawn.
- Use a straight line to join the marked point at the angle to the point vertex of the angle
EVALUATION
- Measure the following angles using your protractor
- a) 880 b)1700 c)2750 d) 3000 e)150
- Construct angle 30o
How to construct Angles Using a Pair of Compasses
600
Procedure
- Draw a straight line and mark the centre O.
- From O, using a convenient radius at point A draw an arc (almost a quadrant).
- With same radius draw another arc to intersect the first arc at C.
- Draw a line from O through the point of intersection.
The angle formed is 600
900
Procedure
- Draw a straight line and mark the centre O.
- From O draw a semicircle to touch the straight line at A and B.
- From A, with longer radius, draw an arc at the centre up.
- From B, with longer radius, draw an arc at the centre up to intersect at C.
- Draw a line from O through C.
The angle COA and COB is 900
BISECTION OF ANGLES
To bisect a given angle
- Draw a given angle ABC.
- With centre B and any convenient radius draw an arc to cut AB to D and BC at E.
- With centre A1 and any small radius an arc.
- With centre E and the same radius draw an arc to intersect the previous one at F.
- Join BD, BD bisects angle ABC, i.e. angle ABD= DBC.
- Use a protractor to check angles ABF and CBF.
The following angles can be constructed by bisection:
- 300 can be constructed by bisecting 600
- 150 can be constructed by bisecting 300
- 12.50 can be constructed by bisecting 150
- 450 can be constructed by bisecting 900
- 22.50 can be constructed by bisecting 450
READING ASSIGNMENT
‘Read about TRIANGLES’
- MELROSE, Basic Science and Technology, Book 2 page 77-79
- NERDC-BASIC TECHNOLOGY, BOOK 2, page 46- 51
WEEKEND ASSIGNMENT
- The angle that FC makes when constructed perpendicular with line AB is _______ (a) 1800 (b) 2700 (c) 900 (d) 1200
- The line FC is called __________ (a) vertical (b) perpendicular (c) Horizontal (d) incline
- Which of the following drawing materials cannot be used to construct a straight line? (a) Compass (b) protractor (c) Ruler (d) pencils
- Angles that sum up to 1800 is called __________ (a) supplementary (b) complementary (c) Reflex (d) obtuse
- The line for all visible outlines is called ____________ (a) Thin continuous line (b) Thick continuous line (c) short dashes (d) Zig – Zag lines.
THEORY
- With the aid of a protractor measure the following angles
(a)150 (b)700 (c)1500 (d)2200 (e)3000.
- With the aid of compasses and a ruler construct angle 600 and 300
