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Trignometry

sneha kulkarni's Avatar
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4 Jun 2007 22:19:11 IST
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trignometry....
None

if tan 1 , tan 2 , tan 3 and tan 4 are the roots of the equation
X4 - X3 sin 2 +  X2 cos 2  - X cos  - sin  = 0
then tan (1+2+3+4) is equal to......
a)sin
b) cos
c) tan
d) cot


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ravi tej's Avatar

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4 Jun 2007 22:52:30 IST
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the ans is cot and the required tan is undefined for sin=1/2 and sin=0
if u want to know how/?
reply to this!
 
sneha kulkarni's Avatar

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4 Jun 2007 22:54:22 IST
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ya....can u explain??
geethu's Avatar

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4 Jun 2007 23:09:47 IST
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from given eqn , sum of roots tan = sin 2
sum of product of 2 roots at a time =tan1tan2 = cos 2
 tan1 tan2 tan3 = cos
tan1 tan2 tan3 tan4 = -sin
tan (1 +2) = (tan1+ tan2 )/(1 - tan1 tan2)
use same formula 2 add tan (3 + 4), again use d same & simplify,
tan { (1 + 2) + (3 + 4) } = (tan  - tan1tan2tan3) / (1-                                             tan1tan2tan3tan4 - tan1tan2)
                                          = (sin2 - cos ) /(1+sin  -cos 2)
                                          = (2sincos  - cos )/(1 +sin  -(1 - 2sin2))
                                          =cot
ravi tej's Avatar

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Joined: 29 May 2007
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4 Jun 2007 23:10:39 IST
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  yeah  sure
if you know this,then it is well & good
else learn it now
tan(x+y+z+..........)=(t1-t3+t5-...........................)/((t0-t2+t4-.............)
 
where tn is sum of tangents taken n at a timme
for ex. in tan(x+y+z),t2 is tanxtany+tanytanz+tanztanx
and t0 is 1
hence tan (1+2+3+4) is t1-t3/1-t2+t4
since t1 is sin2x and t2 is cos2x and t3 is cosx and t4
is -sin2x by simple trasformations we get the required result
geethu's Avatar

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4 Jun 2007 23:14:31 IST
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req tan = cot
when sin  = 0 cot  is infinity and hence req tan is not defined
during simplification trem (2sin - 1) is cancelled,if sin =1/2 ,d term bacomes 0 and cant be cancelled
hope u got it
Himanshu's Avatar

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4 Jun 2007 23:15:06 IST
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good answers :)
Bipin Dubey's Avatar

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5 Jun 2007 07:49:49 IST
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Good work irlmarks and lazycol.

Remember :
tan(x1+x2+x3+......) = (T1 - T3 + T5 ........) / (1 - T2 + T4 ......)
where , Tr is the sum of tangents taken r at a time.

So, tan(1+2+3+4) = (T1 - T3) / (1 - T2 + T4)= (sin2 - cos ) / (1- cos 2 - sin)
tan(1+2+3+4)  = (2sincos - cos) / (2sin2 - sin)
tan(1+2+3+4)  = (cos)(2sin-1) / (sin)(2sin - 1) = cot

Since we are cancelling 2sin
-1 , 2sin-1 0.
Also for =0 , cot would be undefined.



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