1answer is 15 ????
evaluate-
cot^{2}\left(\frac{\pi }{11} \right)+cot^{2}\left(\frac{2\pi }{11} \right)+cot^{2}\left(\frac{3\pi }{11} \right)+cot^{2}\left(\frac{4\pi }{11} \right)+cot^{2}\left(\frac{5\pi }{11} \right)
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6 Answers
1see this
it is one of treasure of my collection of prophet sir's post
http://www.goiit.com/posts/list/trignometry-trigonometry-62432.htm
[1]
1well.....u shud not hav given teh link..... :(
oders may hav being trying(i guess so [3])
1tan (n\theta) =\frac{ntan\theta -^{n}C_{3}tan^{3}\theta +^{n}C_{5}tan^{5}\theta -^{n}C_{7}tan^{7}\theta +....}{1-^{n}C_{2}tan^{2}\theta +^{n}C_{4}tan^{4}\theta ......}
i guess u din get this
exp of tan nθ.....through demoiviers theorem
i guess rest is quiet obvious in teh soln