Question

CotÏ/20â¢cot3Ï/20â¢cot5Ï/20â¢cot7Ï/20â¢cot9Ï/20

Answer 1

AS mentioned in a comment above

tanθ=sinθcosθ.tan⁡θ=sin⁡θcos⁡θ.

then your L.H.S becomes

sinθcosθ.sinθ+cosθsin⁡θcos⁡θ.sin⁡θ+cos⁡θ

from this can you add the terms together? and use sin2θ+cos2θ=1