Example 15 - Chapter 3 Class 11 Trigonometric Functions

Last updated at August 11, 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 (ฯ€/4+๐‘ฅ) + cos (ฯ€/4โˆ’๐‘ฅ) = โˆš2 cos ๐‘ฅ Solving L.H.S. cos (ฯ€/4+๐‘ฅ) + cosโก(ฯ€/4โˆ’๐‘ฅ) = 2 cos ((ฯ€/4 " + " ๐‘ฅ + ฯ€/4 " โˆ’ " ๐‘ฅ )/2) cos ((ฯ€/4 " + " ๐‘ฅ โˆ’ (ฯ€/4 " โˆ’ " ๐‘ฅ) )/2) = ๐Ÿ ๐’„๐’๐’”โก๐›‘/๐Ÿ’ ๐’„๐’๐’”โก๐’™ = 2 ร— 1/โˆš2 cosโก๐‘ฅ = โˆš๐Ÿ ๐’„๐’๐’”โก๐’™ = R.H.S.

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