What am I doing wrong?

  • Thread starter powp
  • Start date
91
0
Hello

I have to prove that

(cos 3x - Cos 7x) / (Sin 3x + Sin 7x) = Tan 2x

So this is what I am doing

-2 Sin (3x + 7x)/2 Sin (3x-7x)/2
--------------------------------
2 Sin (3x + 7x)/2 Cos (3x-7x)/2

-2 Sin 5x Sin -2x
-----------------
2 Sin 5x Cos -2x

Sin 2x
-------
-cos 2x

Which equals -Tan 2x. What am i doing wrong??

Thanks
 
147
1
-2 Sin 5x Sin -2x
-----------------
2 Sin 5x Cos -2x

Sin 2x
-------
-cos 2x
Cos(-2x)=Cos(2x)
Then i believe everything is ok.
 
91
0
Thanks for your help.
 

Related Threads for: What am I doing wrong?

  • Posted
Replies
2
Views
1K
  • Posted
Replies
6
Views
2K
Replies
4
Views
1K
Replies
5
Views
2K
Replies
1
Views
4K
Replies
4
Views
7K
Replies
2
Views
842
Replies
3
Views
702

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top