give a girl a helping hand (1 Viewer)

[P.T.F.E]

i have an assessment tomorrow and i was wondering does anyone have any questions they can post 4 me that are similar too

express cos4@ in terms of cos@ where z=cos@ + isin@

and if u have any handy hints for the exam please feel free cause i have no hope with it.

THANKS

 

[gcchick]

Hey, here's what I came up with:

Based on De Moivre's theorem:
if z = cos@ + isin@,
z^4 = (cos@ + isin@)^4

By expanding using binomial theorem:
z^4 = cos^4@ + 4cos^3@isin@ - 6cos^2@sin^2@ - 4cos@isin^3@ + sin^4@

Equating real and imaginary parts (ie don't include parts that have "i" in them):
cos 4@ = cos^4@ - 6cos^2@sin^2@ + sin^4@

Hope this helps

EDIT: Shit, I misread your post, sorry. I hope this helped anyway, my apologies!

 

[P.T.F.E]

thats ok. i just can't find any similar questions and desperatly need to practice as teacher gave a massive hint in class.

 

[Timothy.Siu]

just read over the textbook and make sure u know the basics,
do some past papers of your school exam if u can or if not just pick out some out of every chapter (complex?) and try to do the hard ones (and maybe an easy one too) just to revise

as for similar questions, look in ur textbook?

or
how bout

from patel

express cos⁵@ in terms of multiples of @ and hence integrate

S cos⁵ @ d@

u can do the same for sin⁵@

 

[P.T.F.E]

THANKS
i have been thru mountains of papers and questions and havnt come across similar questions to that, its in my notes. i will keep burrowingaway at questions.

 

[P.T.F.E]

what about sin5@ in terms of sin@ any one have any solutions

 

[tommykins]

expand z^5 = (cosx + isin)^5 then collect the imaginary terms.

 

[Timothy.Siu]

expand z^5 = (cosx + isin)^5 then collect the imaginary terms.

nice solution

 

[tommykins]

nice solution

i only provide solutions to something that can confuse people.

it's better to give them a hint and they can try it out.

spoon feeding solutions = lame.

 

[P.T.F.E]

i have already done the question i just wanna see if i got the right answer and i dont wanna post it up incase im wrong.