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Ex 6.3, 3 Find the local maxima and local minima, if any, of the following functions. Find also the local maximum and the local minimum values, as the case may be: (iii) β„Ž(π‘₯)=sin⁑π‘₯+cos⁑π‘₯, 0<π‘₯<πœ‹/2 β„Ž(π‘₯)=sin⁑π‘₯+cos⁑π‘₯, 0<π‘₯<πœ‹/2 Finding 𝒉′(𝒙) β„Žβ€²(π‘₯)=𝑑(sin⁑π‘₯ + cos⁑π‘₯" " )/𝑑π‘₯ β„Ž^β€² (π‘₯)=cos⁑π‘₯βˆ’sin⁑π‘₯ Putting 𝒉′(𝒙)=𝟎 cos⁑π‘₯βˆ’π‘ π‘–π‘›π‘₯=0 cos⁑〖π‘₯=𝑠𝑖𝑛 π‘₯γ€— 1 = sin⁑π‘₯/cos⁑π‘₯ 1 = tan π‘₯ tan π‘₯=1 ∴ π‘₯=45Β°= πœ‹/4 Finding h’’(𝒙) h’(π‘₯)=cos⁑π‘₯βˆ’sin⁑π‘₯ h’’(π‘₯)=βˆ’sin⁑π‘₯βˆ’cos⁑π‘₯ Putting 𝒙=𝝅/πŸ’ h’’(Ο€/4)=βˆ’sin(Ο€/4)βˆ’π‘π‘œπ‘ (Ο€/4) = – 1/√2βˆ’1/√2 = (βˆ’2)/√2 = – √2 Since h’’(π‘₯)<0 when π‘₯=Ο€/4 ∴ π‘₯=Ο€/4 is point of Local Maxima f has Maximum value at 𝒙=𝝅/πŸ’ f(π‘₯)=𝑠𝑖𝑛π‘₯+π‘π‘œπ‘ π‘₯ f(Ο€/4)=𝑠𝑖𝑛(Ο€/4)+π‘π‘œπ‘ (Ο€/4) = 1/√2+1/√2 = 2/√2 = √𝟐

  1. Chapter 6 Class 12 Application of Derivatives
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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 14 years. He provides courses for Maths, Science and Computer Science at Teachoo