# simple trigonometry problem

Discussion in 'Mathematics and Physics' started by bloody-orc, Apr 16, 2007.

1. ### bloody-orcNew Member

Joined:
Aug 23, 2004
Messages:
723
Likes:
4
Location:
Estonia
cos(2*x)+cos(4*x) = cos(x);

How to solve this...
It's too late and i just cant figure it out...
i know x should = 1/2 Pi. but cant figure out how the hell to get that

2. ### PapabravoWell-Known Member

Joined:
Mar 9, 2006
Messages:
2,889
Likes:
25
Location:
Michigan, USA (GMT-5)
Since the identity is not generally true, but only true for a particular value it reduces upon substitution to:

+1 + (-1) = 0

There is no general method that I know of for solving this kind of problem since it involves transcendental functions.

3. ### bloody-orcNew Member

Joined:
Aug 23, 2004
Messages:
723
Likes:
4
Location:
Estonia
Last edited: Apr 17, 2007

Joined:
Jan 12, 1997
Messages:
-
Likes:
0

5. ### PapabravoWell-Known Member

Joined:
Mar 9, 2006
Messages:
2,889
Likes:
25
Location:
Michigan, USA (GMT-5)

Truly, Estonians like Elbonians have dizzying intellects!

6. ### ericgibbsWell-Known MemberMost Helpful Member

Joined:
Jan 4, 2007
Messages:
21,240
Likes:
645
Location:
Ex Yorks' Hants UK
ONLINE
hi,

I know papabravo dosn't need me to back him up, BUT the solution to your
problem did come from a States side web source!

Give credit, where credit is due.

Regards.

7. ### bloody-orcNew Member

Joined:
Aug 23, 2004
Messages:
723
Likes:
4
Location:
Estonia
the solutions were uploaded by me... freewebtown just gives me space to post my intelligence And my remarks were not to offend anyone. especially Americans. You have much better university system than we do (yours just costs 450 000\$ more). All they teach us is theory, but there it's all the other way around. more practical things and less "jibba-jabba"

8. ### PapabravoWell-Known Member

Joined:
Mar 9, 2006
Messages:
2,889
Likes:
25
Location:
Michigan, USA (GMT-5)
I was by no means offended, but I also don't feel stronly motivated to check your results. I'll be happy to stipulate that they are completely beyond my graduate level mathematics background. Like I said, you have a truly dizzying intellect. My head is still spinning. I am reminded of a particularly pedantic problem on my fresshman calculus exam.
Code (text):

Take the derivative of

y = tan(x) ^ tan(x) ;

In an engineering career spanning 40 years I've never found a use for that one.

Last edited: Apr 17, 2007