Triangles

CONTENT

Triangles

Types of triangles

Construction of triangles

TRIANGLE

A triangle is a plane figure bounded by three straight lines and having three angles. The sum of angles in a triangle is 180⁰

TYPES OF TRIANGLES

1. Scalene triangle: – This is a triangle that has none of its sides or angles equal.
2. Isosceles triangle: – This is a triangle that has two sides and two angles equal.
3. Equilateral triangle: – This is a triangle that has all the three sides and angles equal.
4. Right-angled triangle: – This is a triangle that one of its angles equal to 90⁰ and the longest line facing the 90⁰ is called THE HYPOTENUSE

EVALUATION

1. What is a triangle?
   1. List the types of triangles and describe them.

TO CONSTRUCT A TRIANGLE GIVEN THE THREE SIDES

Procedure

1. Draw the horizontal line and mark off the base of the triangle AB.
2. With center A and a radius equal to the length of a side of the triangle, strike an arc
3. With center B and a radius equal to the other side strike another arc to cut the previous one at C.
4. Join CA and CB to obtain the triangle ABC.

EVALUATION

Construct triangle ABC such that AB is 8cm BC 7cm and AC is 6cm

TO CONSTRUCT A TRIANGLE GIVEN TWO SIDES AND THE INCLUDED ANGLE

1. Draw a horizontal line and mark off one of the given sides AB
2. At A, construct the given included angle BAC with the aid of a protractor
3. With center A and radius equal to the other given side of the triangle cut AC at D.
4. Join DB to complete the required triangle ABD

EVALUATION

Construct triangle ABC such that line AB is 5cm, <ABC is 60⁰ and line BC is 7cm

TO CONSTRUCT AN EQUILATERAL TRIANGLE USING COMPASSES

1. Draw a horizontal line and mark off base AB equal to the given side.
2. With centers A and B and a radius equal to the given side, strike arcs to intersect at C.
3. Join CA and CB to obtain the required equilateral triangle.

EVALUATION

1. Construct an equilateral triangle whose sides are 6cm long.
   1. Construct triangle ABC such that line AB is 5cm, <ABC is 60⁰ and line BC is 7cm

READING ASSIGNMENT

Read about “CIRCLES”

1. MELROSE, Basic Science and Technology, Book 2 page 73-76
   1. NERDC, BASIC TECHNOLOGY, BOOK 2, page 40- 46

WEEKEND ASSIGNMENT

1. Which of the following triangles has all its sides equal? (a) Equilateral (b) Scalene (c) Isosceles (d) Right-angled
2. Which of the following triangles has none of its side equal? (a) Equilateral (b) Scalene (c) Isosceles (d) Right-angled
3. Which of the following triangles has all two sides equal? (a) Equilateral (b) Scalene (c) Isosceles (d) Right-angled
4. What is the center rule formula used to construct a polygon as well as dividing a circle into equal parts? (a) 360 – N (b) 360 x N (c) ³⁶⁰/ _N (d) 360 + N
5. The perpendicular distance from the vertex to the base of triangles is called ______(a) vetoed (b) Aptitude (c) Altitude (d) Interior

THEORY

1. Construct a rectangle of length 7cm and breadth 5cm with the aid of compass and ruler.
2. Construct a square with diagonal 5cm.