Triq Q (1 Viewer)

[ChemicalChimera]

Hey guys I hope you can help me out a bit on this question.

Solve for x:

cosx = cos4x

Domain: 0 < or equal to x < or equal to pi

Working out would be great thanks!

 

[HeroicPandas]

Use the general solution for cosine:



Where 'n' is an integer



EDIT: It should be:

If cos(A) = cos(B)

Then, A = +/- B + 2k (pi)

 

[21HighStreet]

Hmmm....i'm stuck on this question as well........need help too!

 

[21HighStreet]

What was your working?

 

[21HighStreet]

Show me some working, or I'll Dugong you and turn you into a durian!!!

 

[AnimeX]

Hey guys I hope you can help me out a bit on this question.

Solve for x:

cosx = cos4x

Domain: 0 < or equal to x < or equal to pi

Working out would be great thanks!

try using cos2x=2cos^2(x)-1

ie, cos4x = 2cos^2(2x) -1 = 2(cos^2(x))^2-1
should come out as a polynomial.

 

[funnytomato]

Use the general solution for cosine:



Where 'n' is an integer

+1

you should be able to get 4 solutions from HeroicPandas' method

 

[funnytomato]

if you'd like to use the double angle formula, the polynomial you get is a quartic

 

[braintic]

See solution here: View attachment cosx = cos4x.pdf