# Example 15 - Chapter 3 Class 11 Trigonometric Functions

Last updated at May 29, 2018 by Teachoo

Last updated at May 29, 2018 by Teachoo

Transcript

Example 15 Prove that cos (𝜋/4 + x) + cos (𝜋/4 − 𝑥) = root(2) cos 𝑥 Solving L.H.S : cos (𝜋/4 + x) + cos (𝜋/4 − 𝑥) Using 𝑐𝑜𝑠 𝐴+𝐵+𝑐𝑜𝑠 𝐴−𝐵=2𝑐𝑜𝑠 𝐴𝑐𝑜𝑠 𝐵 cos π4+π+cos π4−x=2 cos π4 cos𝑥 = 2 × 1 2 cos𝑥 = 2 cos 𝑥 = R.H.S ∴ L.H.S = R.H.S Hence, Proved

2x 3x formula - Finding value

Chapter 3 Class 11 Trigonometric Functions

Concept wise

- Radian measure - Conversion
- Arc length
- Finding Value of trignometric functions, given other functions
- Finding Value of trignometric functions, given angle
- (x + y) formula
- 2x 3x formula - Proving
- 2x 3x formula - Finding value
- cos x + cos y formula
- 2 sin x sin y formula
- Finding Principal solutions
- Finding General Solutions
- Sine and Cosine Formula

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.