1.1. Knowledge to remember
The triangle ABC has:
– The three sides are: side AB, side AC, side BC.
– The three vertices are: vertex A, vertex B, vertex C.
The three angles are:
Angle of vertex A, sides AB and AC (referred to as angle A);
Angle of vertex B, sides BA and BC (referred to as angle B);
Angle of vertex C, sides AC and CB (referred to as angle C)
A triangle with three acute angles
A triangle has one obtuse angle and two acute angles
A triangle with one right angle and two acute angles (called a right triangle)
b) Bottom and high line
BC is the bottom, AH is the high line corresponding to the BC bottom. The length AH is the height.
1.2. Solving textbook exercises on page 86
Lesson 1 of the textbook page 86:
Name the three angles and three sides of each triangle below:
The three angles are angle A, angle B, angle C
The three sides are AB, AC, BC
The three angles are: angle D, angle E, angle G
The three edges are: DE, DG, EG
The three angles are: angle M, angle K, angle N
The three sides are MK, MN, and KN.
Lesson 2 Textbook page 86:
Show the base and corresponding height drawn in each of the triangles below:
- Triangle ABC: base is AB, corresponding height is CH.
- Triangle DEG: the bottom is EG, the corresponding high is DK.
- Triangle MPQ: base is PQ, corresponding height is MN.
Lesson 3 Textbook page 86:
Compare the area of:
a) Triangle AED and triangle EDH.
b) Triangle EBC and triangle EHC.
c) Rectangle ABCD and triangle EDC.
a) Area of triangle AED = Area of triangle EDH.
b) Area of triangle EBC = Area of triangle EHC.
c) Area of rectangle ABCD = 2 times area of triangle EDC.