Find the principal solution of the trigonometric equation

Posted July 23rd, 2009 by alpha

Trigonometry questions

secx = 2

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Mathematics

On August 12th, 2010 Kumar Sambhav Gupta says:

i want to know every thing about trigonometric equations so that i can make a ppt presentation,

or may be u can tell me where i can get a ppt presentation on trigonometric equations.

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my doubt

On July 23rd, 2009 alpha says:

The principal solutions( which are only 2) of any trigonometric equation always lie between 0 and 2 $\pi$ .

cos x=1/2
x= $\frac{\pi}{3}$
The value of cos in fourth quadrant is also positive.
So, another principal solution can be $\frac{3\pi}{2}+\frac{\pi}{3}=\frac{11\pi}{6}$

But the answer given in the book is $\frac{5\pi}{3}$ .
Why is my answer wrong?
Is there any thing wrong in my procedure?
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``Old theorems never die; they turn into definitions.''
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