Circular functions questions

[Momo.05]

 :tickedoff: :uglystupid2: Okay, there are two questions that i can only solve half of each and i was hoping someone out there can help me out.. before i pull out all my hair that is >:/ .. They look simple but i have no idea how to attempt the second part of both questions ...

Here they are ;

(a) Expand sin(x+2x)
Which equals to sin(x)cos(2x)+cos(x)sin(2x) .. But part (b) is the confusing part... it asks to "express sin3x in terms of sinx" > What does that mean?

Same goes for this question
(a) Expand cos(x+2x)
Which equals cos(x)cos(2x) - sin(x)sin(2x)

(b) Express cos3x in terms of cosx > Not again --"

Do i meant to expand the "cos2x" and "sin2x" or something ?

Thanks for the help on these two questions 

[TrueTears]

Hint to a) which will solve all your problems

Consider double angle formula for cos(2x)

[Momo.05]

Hrmm , okay ..
When i work it out im missing a whole number in front but have cube of the sines if that makes sense :/
But thank you for the hint

[Momo.05]

OHHH wait i think im getting somewhere.. yeah i think i know what you meant .. ahaha thank you thank youuu !
(I might come back even more confuse but i think i got it )

[TrueTears]

OHHH wait i think im getting somewhere.. yeah i think i know what you meant .. ahaha thank you thank youuu !
(I might come back even more confuse but i think i got it )

nps, if you really can't get it I'll post what I did but I think it should be fairly straight forward

[Momo.05]

LOL.. umm "True Tears" ?
Can you post your answers for me please? I done both of questions part a's but my answers for the "expressing in terms of sinx/cosx" is a bit funny...

If you dont mind, can i see how you solved it out ?

(Yeah, im a tad bit slow at the moment ==")

Oh by the way your picture of "Kyou" sure looks like a character from kanon, just a random thought that crossed my mind for a second

[TrueTears]

sin(x)cos(2x)+cos(x)sin(2x)

cos(2x) = 1-2sin^2(x)

sin(x)(1-2sin^2(x))+cos(x)2sin(x)cos(x)

sin(x)-2sin^3(x)+cos^2(x)2sin(x)

sin(x)-2sin^3(x)+(1-sin^2(x))2sin(x)

sin(x)-2sin^3(x)+2sin(x)-2sin^3(x)

3sin(x)-4sin^3(x)

Note: because my computer is fucked up and freezes every few seconds, I cbf'ed latexing hopefully you can read that

Note 2: close guess, seems like kanon since the same company made both animes, its actually from clannad.

[Momo.05]

Thank you, umm yeah no problem i can read it
I guess i was sorta, semi-not really on the right track with my working out this is really a life saver, i still have half my hair left ! (Its suppose to be a joke from before.. but if u dont get it i cant blame u im horrible at making jokes.. but thanks again !)

And yeah the art is really similar.. but then all anime girls look similar LOL
Oh and dw about ur com.. im capped LOLS

[TrueTears]

lolz, its good pulling out heaps of hairs, that what i currently do reading number theory.

pulling out hair + maths go hand in hand.

[Momo.05]

Agree, and morning to you. (currently 12 00 am )
Hope you have a agreat day and if u ever wonder again to another question on this forum would be glad if u can help me out again like today

[TrueTears]

lol, whereever there is maths you will see me there

I won't miss it.

Never.