IIT JEE , AIEEE Forum - Mathematics , Algebra

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p.t sin5

/sin

= 16cos⁴

-12cos²

+1

and show that solutions of z^4-3z^2+1=0 are 2cospi/5, 2cos2pi/5, 2cos3pi/5,2cos4pi/5

also deudce that 2cospi/5 = 1+root(5)/2 , 2cos2pi/5 = -1+root(5)/2

give full solution.

konichiwa2x

Well, I am quite flattered that you ask for me directly. But do adress your question to everyone if you wish to get more replies.

For the first question you could always proceed using the trigonemtric identity

. But thats boring!

So instead, Put

Now put

in RHS and see what that tells u.

if and only if

and

Hence solutions are

. Got it?

For your second question, see that completeting the square gives.

. Also note that

.
Also note that

for

and

for

And by the way it is konichiwa not koichniwa!

by the way how do u know me? I see you are new to the website.

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my friend