## Introduction to Trigonometry

*Short Q and A*

**Q1: If sin 3A = cos (A – 26°), where 3A is an acute angle, find the value of A.**

Answer: sin 3A = cos (A – 26°)

∵ sin 3A = cos (90° – 3A)

∴ cos (90° – 3A) = cos (A – 26°)

Since

90° – 3A and A – 26° are both acute angles, therefore,

90° – 3A = A – 26°

⇒ A = 29°

**Q2: Express cot 85° + cos 75° in terms of trigonometric ratios of angles between 0° and 45°.**

Answer: cot 85° + cos 75° = cot (90° – 5°) + cos (90° – 15°)

= tan 5° + sin 15°