Triangles JSS2 Basic Technology Lesson Note

TOPIC: 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 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?
2.         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 of 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. 
2.         Construct triangle ABC such that line AB is 5cm, <ABC is 600, and line BC is 7cm