Page 156 - New Medley 5 Semester 2

In scalene triangle XYZ, all the three sides are unequal. i.e., XY ≠ YZ
≠ XZ

Classification of Triangles on the Basis of Angles

On the basis of angles, triangles are categorised into three groups. These
are:
A

1. Acute-angled triangle: A triangle having all the angles 60°
are acute, i.e., 90°, is called acute-angled triangle.

In ∆ABC, A = 60°, B = 70° and C = 50° 70° 50°
B C
Here, all the three angles are acute angle, so ∆ABC is

an acute-angled triangle.
P

2. Right-angled triangle: A triangle in which any one angle
50°
is exactly 90°, i.e., a right angle, is called a right-angled
triangle. In this triangle, the other two angles are acute

angle. 90° 40°
Q R

In ∆PQR, P = 50°, Q = 90° and R = 40°

Therefore, ∆PQR is a right-angled triangle.

3. Obtuse-angled triangle: A triangle in which one angle is greater than
90° is called obtuse-angled triangle. X

In ∆XYZ, X = 30°, Y = 130° 30°
130°
and Z = 20° 20°
Y Z
Therefore, ∆XYZ is an obtuse-angled triangle.

EXERCISE 7.1

A. Draw a rough sketch of each of the following.
1. A polygon with three sides 2. A polygon with four angles

3. A polygon with five sides 4. A polygon with six equal sides

5. A regular polygon with eight sides

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