Exercise 6.3 of Class 9 Maths Chapter 6 Lines and Angles introduces important terms such as exterior angle, linear pair and vertically opposite angles, requiring students to practice this exercise.

NCERT Class 9 Chapter 6 Exercise 6.3 Question No. 4

Page No. 107 & 108

Given that: ∠PRT = 40°, ∠RPT = 95° and ∠TSQ = 75°

In △PTR, ∠P + ∠R + ∠PTR = 180°

⇒ 95° + 40° + ∠PTR = 180°

⇒ 135° + ∠PTR = 180°

⇒ ∠PTR = 180° – 135° = 45°

∠STQ = ∠PTR [∵ Vertically Opposite Angles]

⇒ ∠STQ = 45°

In △SQT, ∠STQ + ∠S + ∠SQT = 180°

⇒ 45° + 75° + ∠SQT = 180°

⇒ 120° + ∠SQT = 180°

⇒ ∠SQT = 180° – 120° = 60°