Trig Identities:

  • Thread starter mathguyz
  • Start date
  • #1
3
0
Everyone knows the obvious trig identities like sin^2 + cos^2 =1, cosx=1+ sin^2, and tanx =sin/cos. I ran across an old identity the other day: 3cos^2(3x)+3sin^2(3x)=3. Can anyone here figure out why and how? I tried it and couldnt figure it out.
 

Answers and Replies

  • #2
jamesrc
Science Advisor
Gold Member
476
1
Look at your first "obvious trig identity"...
 
  • #3
193
0
3cos^2(3x)+3sin^2(3x)=3[cos^2(3x)+sin^2(3x)] , now substitude 3x=z and using sin^2(z) + cos^2(z) =1 you have it!

NB: I´m not sure this is correct, whatever it is meant to be: cosx=1+ sin^2
 

Related Threads on Trig Identities:

  • Last Post
Replies
4
Views
4K
  • Last Post
Replies
13
Views
11K
Replies
7
Views
2K
  • Last Post
Replies
4
Views
3K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
2
Views
10K
  • Last Post
Replies
7
Views
1K
Replies
2
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
3
Views
1K
Top