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 𝐴﷯𝑐𝑜𝑠 𝐵﷯ cos π﷮4﷯+π﷯+cos π﷮4﷯−x﷯=2 cos﷮ π﷮4﷯﷯﷯ cos﷮𝑥﷯ = 2 × 1﷮ ﷮2﷯﷯ cos﷮𝑥﷯ = ﷮2﷯ cos 𝑥 = R.H.S ∴ L.H.S = R.H.S Hence, Proved

Next: Example 16 Important → Ask a doubt

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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