My teacher gave me a question to expand cos4x in ascending powers of x including the x^4 term and I don't understand her solution, which is 1-8x^2 +(32/3)x^4. Can someone explain please?

Question

tkhunny · Answer

Any particular method or formula or process that should be used?

anonymous · Answer

urm, I'm not sure, most likely binomial theorem or something because that's the topic we're on

alekos · Answer

use the taylor series expansion for cosx

anonymous · Answer

okay I'll try it! thanks so much! :)

anonymous · Answer

I tried the Maclaurain's expansion, and it worked! thanks again :)

alekos · Answer

that'll work too

anonymous · Answer

http://www.wolframalpha.com/input/?i=series+cos%284x%29+at+x%3D0

anonymous · Answer

thanks @eliassaab !

anonymous · Answer

YW