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Ask community Community Discussion Question: Find the number of solution of the equation have... |cot x| = cot x + 1/sin x ( 0 < or equal to x
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Nikhil Chaturvedi (30)

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Find the number of solution of the equation have...|cot x| = cot x + 1/sin x ( 0 < or equal to x < or equal to 2(pi) ) ??????????????????????
    
||Mr.Insomaniac|| (91)

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 It has four solutions.

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bond 007 (5)

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 Plz give the solution...............

 

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Deepak Aggarwal (3759)

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|cot(x)| = cot(x)  + 1/sin(x)

|cot(x)| = cot(x)  + cosec(x)

Now, clearly note that |cot(x)|  = cot(x) , when x belongs to 0 to pi/2 or x belongs from pi to 3pi/2

                                                     = - cot(x), when x belongs to pi/2 to pi or x belongs from 3pi/2 to 2pi

CASE1. When x belongs to 0 to pi/2 or x belongs from pi to 3pi/2,

cot(x) = cot(x) + cosec(x)

or, cosec(x) = 0 which is not possible.

 

CASE2. When x belongs to pi/2 to pi or x belongs from 3pi/2 to 2pi

-cot(x) = cot(x) + cosec(x)

(cosec(x))(1 + 2 cos(x)) = 0

cosec(x) # 0

so, 1 + 2cos(x) = 0

or, cos(x) = -1/2

so, x = 2pi/3 (because x belongs to pi/2 to pi or x belongs from 3pi/2 to 2pi)

Hence there is only one solution.

 

 

You can see it from the graph even---

clearly there is only one solution, in 0<x<2pi.

 

 


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||Mr.Insomaniac|| (91)

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@Deepak

It has two solutions as cos(x) = -1/2 has two solutions.

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siDDhESwaR MuKhErjEE (358)

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the first part is alright ie when x lies between o and pie/2 and between pie and 3pie/2..........in this case there are no solution......however when the second part is followed, we will have two solutions for cos x =-1/2.
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Deepak Aggarwal (3759)

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@||Mr.Insomaniac|| and siDDhESwaR MuKhErjEE

You say that cos(x) = -1/2 has two solutions.

But just for a minute check the domain of x for which i have taken the second case. x is in 2nd and 4th quadrant. cos(x) is positive in 4th quadrant. so, there is only one solution i.e. 2pi/3 in 2nd quadrant.

The second solution you are talking about is x = 4pi/3 which lies in third quadrant. So, it is not the solution.

Anyhow i have made the graph there you can clearly see thta there's only one solution.

Hope you agree with me this time.................

 


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||Mr.Insomaniac|| (91)

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 YA GOT THE POINT

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siDDhESwaR MuKhErjEE (358)

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dats true.....i am sorry. There would be one solution. I am sorrry guys.
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