• Support PF! Buy your school textbooks, materials and every day products Here!

Trig identity proof.

  • Thread starter Bradyns
  • Start date
  • #1
20
0
Prove:
[itex]\frac{CosθSinθ}{1 + Tanθ}[/itex] = Cos2θ
===========================
I multiply out the denominator to get:

CosθSinθ = Cos2θ + CosθSinθ

I cannot seem to prove it.

Starting to think it's a trick question.. :/
 

Answers and Replies

  • #2
37
4
It most certainly is a trick question because the supposed identity doesn't even work if you plug in theta = 0. The left side is 0 while the right is 1, in this case!
 
  • #3
296
0
You might be asked to solve the equation instead of proving the identity, and the solutions of the equation are the zeros of cosine, id est odd integer multiples of [itex]\pi/2[/itex].
 

Related Threads for: Trig identity proof.

  • Last Post
Replies
6
Views
1K
  • Last Post
Replies
24
Views
9K
  • Last Post
Replies
2
Views
852
  • Last Post
Replies
12
Views
2K
  • Last Post
2
Replies
27
Views
7K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
11
Views
9K
  • Last Post
Replies
22
Views
3K
Top