**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

** 180**0**- (60**0** + 45**0**)= 75**0

- To construct 1350, combine 450 and 900

** 45**0**+ 90**0** = 135**0

- To construct 1050, combine 600 and 450

** 45**0**+ 60**0** = 135**0

**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 **

**60****0 **

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 60**0**

**90****0**

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 90**0**

**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:

- 30
**0**can be constructed by bisecting 60**0** - 15
**0**can be constructed by bisecting 30**0** - 12.5
**0**can be constructed by bisecting 15**0** - 45
**0**can be constructed by bisecting 90**0** - 22.5
**0**can be constructed by bisecting 45**0**

**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

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