Question

25. If 13theta =pi, find the value ofcos 3theta + cos 5theta + 2 costheta cos 9theta​

Answer 1

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

Step-by-step explanation:

Answer 2

Answer:

ans in attachment mate