Page 187 - ICSE Math 6

On the basis of angles A

• Acute-angled triangle 80°
A triangle in which all the angles are acute angles (less than 90°)
is known as an acute-angled triangle. B 45° 55° C
• Obtuse-angled triangle P
A triangle in which one of the angles is obtuse angle (more than 30°
90° but less than 180°) is known as an obtuse-angled triangle.
• Right-angled triangle 120° 30°

A triangle in which one of the angles is a A Q R
right angle (90°) is known as a right-angled
triangle. In a right-angled triangle, the side Maths Info
opposite to the right angle is the largest side In a right-angled triangle, the
and is known as the hypotenuse. In the other two angles are acute
adjoining figure, AB is the hypotenuse. B C angles.

Example 5: Classify each of the following triangles on the basis of their:
(a) sides (b) angles
P L

A
10 cm 9 cm
5 cm 7 cm 8 cm 7 cm

B 7 cm C Q 6 cm R M 3 cm N
(i) (ii) (iii)

R
D X

6 cm 6 cm 7 cm
4 cm 6 cm

S 6 cm T E 4 cm F Y 6 cm Z

(iv) (v) (vi)

(a) Classification according (b) Classification according
Solution: Figure
to sides to angles

(i) ∆ ABC Isosceles triangle Acute-angled triangle
(ii) ∆ PQR Scalene triangle Right-angled triangle
(iii) ∆ LMN Scalene triangle Obtuse-angled triangle
(iv) ∆ RST Equilateral triangle Acute-angled triangle
(v) ∆ DEF Isosceles triangle Obtuse-angled triangle
(vi) ∆ XYZ Isosceles triangle Right-angled triangle

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