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°
