Question

cos(pi/11)+cos(3pi/11)+cos(5pi/11) + cos(7pi/11) + cos(9pi/11)

Answer 1

It is 1/2

Answer 2

but my answer is not matchig the text

Answer 3

USE COSINE SERIES FORMULAE

Answer 4

@rational

Answer 5

It should bezero , right ?

Answer 6

it is 0.5

Answer 7

It should bezero , right ?

Answer 8

https://www.google.co.in/search?q=cos(pi%2F11)%2Bcos(3pi%2F11)%2Bcos(5pi%2F11)+%2B+cos(7pi%2F11)+%2B+cos(9pi%2F11)&oq=cos(pi%2F11)%2Bcos(3pi%2F11)%2Bcos(5pi%2F11)+%2B+cos(7pi%2F11)+%2B+cos(9pi%2F11)&aqs=chrome..69i57&sourceid=chrome&es_sm=122&ie=UTF-8

Answer 9

does anyone know the cosine series formula

Answer 10

It is to be solved by that method only

Answer 11

Will try ltr my phone acting weird lol i had to switch to laptob to use os

Answer 12

\[\large \begin{align} e^{i \pi/11} + e^{i3\pi/11} + \cdots + e^{i9\pi/11} &= \dfrac{e^{i \pi/11} \left(e^{i 10\pi/11} - 1\right)}{e^{i 2\pi/11} -1} \\~\\ &= \dfrac{e^{i\pi} - e^{i \pi/11} }{(e^{i \pi/11} -1)(e^{i \pi/11} +1)}\\~\\&= \dfrac{-1-e^{i \pi/11}}{(e^{i \pi/11} -1)(e^{i \pi/11} +1)}\\~\\&= \dfrac{1}{1-e^{i\pi/11}}\end{align}\]

Answer 13

not that

Answer 14

is that the series formula you talking about ?

Answer 15

:)

Answer 16

a = pi/11
d = 2pi/11

Answer 17

just plugin and evaluate ?

Answer 18

i m not getting a answer actually

Answer 19

\[\large \dfrac{\sin \left(5\times \pi/11\right)}{\sin \left(\pi/11\right)}\times \cos\left(\dfrac{2\pi/11 + (5-1)2\pi/11}{2}\right)\]

Answer 20

\[\large \dfrac{\sin \left(5\pi/11\right)}{\sin \left(\pi/11\right)}\times \cos\left(5\pi/11\right)\]

Answer 21

use sinAcosB formula

Answer 22

that would be sin 10 pi /11 right

Answer 23

use sin2A formula

Answer 24

yes and with a 1/2

Answer 25

\[\large \dfrac{\sin \left(10\pi/11\right)}{2\sin \left(\pi/11\right)}\]

Answer 26

no wait 1 min

Answer 27

difference is 2pi/11 right

Answer 28

yes d = 2pi/11

Answer 29

n = number of terms in the series = 5

Answer 30

ok got it sry ,
thank you

Answer 31

I am sorry