Chapter 5: Understanding Elementary Shapes

Name the types of following triangles:

(a) Triangle with lengths of sides 7 cm, 8 cm and 9 cm.

(b) ∆ABC with AB = 8.7 cm, AC = 7 cm and BC = 6 cm.

(c) ∆PQR such that PQ = QR = PR = 5 cm.

(d) ∆DEF with ∠D = 90°

(e) ∆XYZ with ∠Y = 90° and XY = YZ.

(f) ∆LMN with ∠L = 30°, ∠M = 70° and ∠N = 80°.

Match the following:

Measures of Triangle Type of Triangle

(i) 3 sides of equal length                                                                                 (a) Scalene

(ii) 2 sides of equal length                                                                                (b) Isosceles right angled

(iii) All sides are of different length                                                             (c) Obtuse angled

(iv) 3 acute angles                                                                                                (d) Right angled

(v) 1 right angle                                                                                                      (e) Equilateral

(vi) 1 obtuse angle                                                                                                  (f) Acute angled

(vii) 1 right angle with two sides of equal length                                       (g) Isosceles

Name each of the following triangles in two different ways: (you may judge the nature of the angle by observation)

Try to construct triangles using match sticks. Some are shown here. Can you make a triangle with

(a) 3 matchsticks?

(b) 4 matchsticks?

(c) 5 matchsticks?

(d) 6 matchsticks?

(Remember you have to use all the available matchsticks in each case)

Name the type of triangle in each case. If you cannot make a triangle, think of reasons for it