Example 15 - Chapter 3 Class 11 Trigonometric Functions

Last updated at July 26, 2026 by

Example 15 - Prove cos (pi/4 + x) + cos (pi/4 - x) = root 2 cos x - Examples

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Example 15 Prove that cos (π/4+𝑥) + cos (π/4−𝑥) = √2 cos 𝑥 Solving L.H.S. cos (π/4+𝑥) + cos⁡(π/4−𝑥) = 2 cos ((π/4 " + " 𝑥 + π/4 " − " 𝑥 )/2) cos ((π/4 " + " 𝑥 − (π/4 " − " 𝑥) )/2) = 𝟐 𝒄𝒐𝒔⁡𝛑/𝟒 𝒄𝒐𝒔⁡𝒙 = 2 × 1/√2 cos⁡𝑥 = √𝟐 𝒄𝒐𝒔⁡𝒙 = R.H.S.

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