Complex Number question (2 Viewers)

[spakfilla]

Came across this question was wondering how to go about solving it using De Moivre's Therorem

Thanks in advance

 

[jyu]

Came across this question View attachment 22638 was wondering how to go about solving it using De Moivre's Therorem

Thanks in advance

Numerator=rcis(pi/14)
Denominator=rcis(-pi/14)
Fraction=cis(pi/7)
(fraction)^7=cis(pi)=-1

 

[spakfilla]

Where do you get the pi/14 from?

 

[jyu]

Plot 1+cis(pi/7) in the complex plane to see it.

 

[jyu]

like this type of questions
you don't do it the usual way

 

[spakfilla]

Yeah...now in totally confused

 

[jyu]

 

[spakfilla]

How would you do it algebraically?
I understand the complex plane method now... thank you

 

[ohexploitable]

You wouldn't do it algebraically because it would make you want to cut your wrists.

Or maybe not, see below.

 

[jyu]

 

[hscishard]

Or you can go cos(pi/7) = 2cos^2 pi/14 - 1 and do the same for sinpi/7. The 1 will cancel out

 

[spakfilla]

Or you can go cos(pi/7) = 2cos^2 pi/14 - 1 a

How do you do that?

 

[AAEldar]

How do you do that?

 

[spakfilla]

LOL....i dont know what is was thinking