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Example 15.jpg

  1. Chapter 3 Class 11 Trigonometric Functions
  2. Serial order wise
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Example 15 Prove that cos (๐œ‹/4 + x) + cos (๐œ‹/4 โˆ’ ๐‘ฅ) = root(2) cos ๐‘ฅ Solving L.H.S : cos (๐œ‹/4 + x) + cos (๐œ‹/4 โˆ’ ๐‘ฅ) Using ๐‘๐‘œ๐‘  ๐ด+๐ต๏ทฏ+๐‘๐‘œ๐‘  ๐ดโˆ’๐ต๏ทฏ=2๐‘๐‘œ๐‘  ๐ด๏ทฏ๐‘๐‘œ๐‘  ๐ต๏ทฏ cos ฯ€๏ทฎ4๏ทฏ+ฯ€๏ทฏ+cos ฯ€๏ทฎ4๏ทฏโˆ’x๏ทฏ=2 cos๏ทฎ ฯ€๏ทฎ4๏ทฏ๏ทฏ๏ทฏ cos๏ทฎ๐‘ฅ๏ทฏ = 2 ร— 1๏ทฎ ๏ทฎ2๏ทฏ๏ทฏ cos๏ทฎ๐‘ฅ๏ทฏ = ๏ทฎ2๏ทฏ cos ๐‘ฅ = R.H.S โˆด L.H.S = R.H.S Hence, Proved

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