anonymous
  • anonymous
how to find value of sin 18.......plz explain in detail
Trigonometry
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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anonymous
  • anonymous
without the use of the calculator?
anonymous
  • anonymous
ya
anonymous
  • anonymous
how 2 derivate it

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anonymous
  • anonymous
taylor expansion can estimate it for you
anonymous
  • anonymous
i did not get what u want to say
anonymous
  • anonymous
sauravshakya u may try
anonymous
  • anonymous
who is taylor
anonymous
  • anonymous
Taylor Expansion is the way of estimating and function sinx is \[x-\frac{ x ^{3} }{ 6 }+\frac{ x ^{5} }{ 120 } -...+...\]
anonymous
  • anonymous
5*18=90 sin(5*18)=sin90 Let x=18 then, sin(5x)=sin90
anonymous
  • anonymous
i think u r wrog somewhere
anonymous
  • anonymous
U can proceed from here but this will be too long but it will give u exact value.
anonymous
  • anonymous
we dont have a formula for sin 5 thete
anonymous
  • anonymous
From sin(5x)=1 u need to find the value of sinx
anonymous
  • anonymous
i mean to say we dont have its expansion
anonymous
  • anonymous
sin(5x) = sin(2x + 3x) = sin2x * cos3x + cos2x * sin3x
anonymous
  • anonymous
hmmmmm that wd be 22 long
anonymous
  • anonymous
5x= 90 2x+3x=90 3x=90-2x sin 3x= cos 2x now put formula of sin 3x and cos 2x in terms of sin x only.
anonymous
  • anonymous
hmmmmmm this wd b an easy one
anonymous
  • anonymous
18=Pi/10 sin(Pi/10)=0.3090169944 F[x]\[=x-\frac{ x ^{3} }{ 6 }+\frac{ x ^{5} }{ 120 }-... \] f[Pi/10]==0.3090170542 you decide
anonymous
  • anonymous
Great!
anonymous
  • anonymous
but when we will solve the quadrtic equation then we will get two values of sin theta
anonymous
  • anonymous
which one is great
anonymous
  • anonymous
@gohangoku58 's one
anonymous
  • anonymous
hmmmmmmm
anonymous
  • anonymous
because that gives exact value not approximate
anonymous
  • anonymous
hmmmmm but two values
anonymous
  • anonymous
which one to select
anonymous
  • anonymous
u plz try it once
anonymous
  • anonymous
well, sin 18 lies in first quadrant so take positive value
anonymous
  • anonymous
hmmmmm
anonymous
  • anonymous
good
anonymous
  • anonymous
u'll get a cubic equation, with one root = 0 (can't be, rejected) and 2 other roots.....from which u select one with positive value..... like saura said...
anonymous
  • anonymous
i failed 2 use common sence
anonymous
  • anonymous
no not a cubic but a quadratic u try it
anonymous
  • anonymous
i tried it jjust now
anonymous
  • anonymous
sin 3x= ?
anonymous
  • anonymous
3sinx-4 sin cube x
anonymous
  • anonymous
3sinx-4 sin cube x<----cubic
anonymous
  • anonymous
no but sin 2 x is also there
anonymous
  • anonymous
*cos 2x
anonymous
  • anonymous
ya
anonymous
  • anonymous
1-2sin square x
anonymous
  • anonymous
then we can take sin in common
anonymous
  • anonymous
no u cant 1 is there
anonymous
  • anonymous
r u there on facebook
anonymous
  • anonymous
who ?
anonymous
  • anonymous
sorry for the personal Q
anonymous
  • anonymous
we both are there...
anonymous
  • anonymous
all of u
anonymous
  • anonymous
|dw:1353245978780:dw|
anonymous
  • anonymous
may i know ur id's
anonymous
  • anonymous
we can contact there also
anonymous
  • anonymous
saura i will tell u wait
anonymous
  • anonymous
what say saura ?
anonymous
  • anonymous
short form
anonymous
  • anonymous
4 x^3 - 2 x^2 - 3x + 1 = 0 one root is x=1 which can't be.... i made a typo earlier and wrote that one root is 0
anonymous
  • anonymous
one moment plzz
anonymous
  • anonymous
2 theta=90-3 theta
anonymous
  • anonymous
sin 2 theta = cos 3 theta.................sin (90-theta)=costheta

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