Class 11th Maths – RD Sharma Chapter 8 : Trigonometric Formulae – Exercise 8.1 Solutions (Step-by-Step Guide)

1. Express each of the following as the sum or difference of sines and cosines: (i) 2 sin 3x cos x (ii) 2 cos 3x sin 2x (iii) 2 sin 4x sin 3x (iv) 2 cos 7 x cos 3x Watch Solution
2. Prove that: 2 sin 5π/12 sin π/12 = 1/2 Watch Solution
3. Prove that: 2 cos 5π/12 cos π/12 = 1/2 Watch Solution
4. Prove that: 2 sin (5π/12) cos (π/12) = (√3 + 2)/2 Watch Solution
5. Show that: sin 50° cos 85° = (1 − √2 sin 35°) / (2√2) Watch Solution
6. Show that: sin 25° cos 115° = 1/2(sin 140° – 1) Watch Solution
7. Prove that: 4 cos x cos (π/3 + x) cos(π/3 – x) = cos 3x Watch Solution
8. Prove that: cos 10° cos 30° cos 50° cos 70° = 3/16 Watch Solution
9. Prove that: cos 40° cos 80° cos 160° = – 1/8 Watch Solution
10. Prove that: sin 20° sin 40° sin 80° = √3/ 8 Watch Solution
11. Prove that: cos 20° cos 40° cos 80° = 1/8 Watch Solution
12. Prove that: tan 20° tan 40° tan 60° tan 80° = 3 Watch Solution
13. Prove that: tan 20° tan 30° tan 40° tan 80° = 1 Watch Solution
14. Prove that: sin 10° sin 50° sin 60° sin 70° = √3/16 Watch Solution
15. Prove that: sin 20° sin 40° sin 60° sin 80° = 3/16 Watch Solution
16. Show that: sin A sin (B – C) + sin B sin (C – A) + sin C sin (A – B) = 0 Watch Solution
17. Show that: sin (B – C) cos (A – D) + sin (C – A) cos (B – D) + sin (A – B) cos (C – D) = 0 Watch Solution
18. If α + β = π/2, show that the maximum value of cos α cos β is 1/2. Watch Solution
19. Prove that: tan x tan(π/3 − x) tan(π/3 + x) = tan 3x Watch Solution

Chapter 8: Transformation Formulae – R. D. Sharma Class 11th Maths

1. Transformation Formulae Exercise 8.1 Video Solution

2. Transformation Formulae Exercise 8.2 Video Solution

3. Transformation Formulae Multiple Choice Questions (MCQs) Video Solution Video Solution

4. Transformation Formulae Fill in the Blanks (FBQs) Video Solution

5. Transformation Formulae Very Short Answer Questions (VSAQs) Video Solution Video Solution