If 13θ= π , find the value of 3θ+cos5θ + 2cosθcos9θ

Asked by tps.mjmdr | 16th Jun, 2018, 05:40: PM

Expert Answer:

 cos3θ+cos5θ + 2cosθcos9θ
begin mathsize 16px style 13 straight theta equals straight pi rightwards double arrow straight theta equals straight pi over 13
cos 3 straight theta plus cos 5 straight theta plus 2 cosθcos 9 straight theta
equals cos 3 straight theta plus cos 5 straight theta plus cos 10 straight theta plus cos 8 straight theta
equals cos fraction numerator 3 straight pi over denominator 13 end fraction plus cos fraction numerator 5 straight pi over denominator 13 end fraction plus cos fraction numerator 10 straight pi over denominator 13 end fraction plus cos fraction numerator 8 straight pi over denominator 13 end fraction
equals cos fraction numerator 3 straight pi over denominator 13 end fraction plus cos fraction numerator 10 straight pi over denominator 13 end fraction plus cos fraction numerator 5 straight pi over denominator 13 end fraction plus cos fraction numerator 8 straight pi over denominator 13 end fraction
equals cos fraction numerator 3 straight pi over denominator 13 end fraction plus cos open parentheses straight pi minus fraction numerator 3 straight pi over denominator 13 end fraction close parentheses plus 2 cos straight pi over 2 cos fraction numerator 5 straight pi over denominator 26 end fraction
equals cos fraction numerator 3 straight pi over denominator 13 end fraction minus cos fraction numerator 3 straight pi over denominator 13 end fraction plus 0
equals 0 end style
 
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Answered by Sneha shidid | 19th Jun, 2018, 11:39: AM

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