In ∆ ABC, BC = AB and ∠B = 80°. Then ∠A is equal to
a. 80°
b. 40°
c. 50°
d. 100°

Solution:

From the question,

In ∆ ABC, BC = AB and ∠B = 80°

As BC = AB, ∆ ABC is an isosceles triangle

Consider ∠C = ∠A = x

∠B = 80° [Given]

Using the angle sum property

We know that the sum of interior angles of a triangle = 180°

∠A + ∠B + ∠C = 180°

Let us substitute the values

x + 80° + x = 180°

2x = 180° - 80°

2x = 100°

Dividing both sides by 2

x = 50°

Therefore, ∠A is equal to 50°.

✦ Try This: In ∆ PQR, QR = PQ and ∠Q = 50°. Then ∠A is equal to a. 30°, b. 50°, c. 80°, d. 65°

☛ Also Check: NCERT Solutions for Class 9 Maths Chapter 7

NCERT Exemplar Class 9 Maths Exercise 7.1 Problem 4

In ∆ ABC, BC = AB and ∠B = 80°. Then ∠A is equal to , a. 80° , b. 40° , c. 50°, d. 100°

Summary:

Angle sum property states that the sum of interior angles of a triangle equals 180°. In ∆ ABC, BC = AB and ∠B = 80°. Then ∠A is equal to 50°

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