I need help on identities

  • Thread starter Mathslova
  • Start date
  • #1
7
0
Can someone kindly help to find the exact values of cosx and sinx when tanx=2..:redface:
 

Answers and Replies

  • #2
Moonbear
Staff Emeritus
Science Advisor
Gold Member
11,490
52
Please show your own work on the problem so far so that the homework helpers know where to begin with helping you on this.
 
  • #3
7
0
well i could have done it easily if it was in half angle form..i.e tan(1/2x)=2...i have some formulae to use but for that one i have no idea how to start
 
  • #4
robphy
Science Advisor
Homework Helper
Insights Author
Gold Member
5,779
1,078
In what kind of problem might the expression tan x=2 occur?
 
  • #5
cristo
Staff Emeritus
Science Advisor
8,107
73
You don't really need a formula as such. Try drawing a diagram (i.e. a right angled triangle). You know the value of the tangent of one angle, so you should be able to write down the values of two of the sides. There's a theorem that you know to find the third side-- try using this.
 
  • #6
arildno
Science Advisor
Homework Helper
Gold Member
Dearly Missed
9,970
133
Well, the simplest way is to utilize the identity:
[tex]\tan^{2}(x)+1=\frac{1}{\cos^{2}(x)}[/tex]
If you are not familiar with that result, you should try to prove it first.
 
  • #7
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,621
6
You don't need any identities to solve the system. Start by finding x...
 
  • #8
7
0
You don't really need a formula as such. Try drawing a diagram (i.e. a right angled triangle). You know the value of the tangent of one angle, so you should be able to write down the values of two of the sides. There's a theorem that you know to find the third side-- try using this.
Very much appreciated...I used SOHCAHTOA and got the answer I was looking for:smile:
 
  • #9
HallsofIvy
Science Advisor
Homework Helper
41,833
962
Yes, Cristo's answer was the simplest method.

(Darn, he got it in ahead of me!)
 
  • #10
robphy
Science Advisor
Homework Helper
Insights Author
Gold Member
5,779
1,078
Ideally, the OP would have used my hint.
 
  • #11
HallsofIvy
Science Advisor
Homework Helper
41,833
962
In what kind of problem might the expression tan x=2 occur?
Ideally, the OP would have used my hint.
I understand your point, but I can think of many problems involving tan x= 2 (or other values of tan x) that have nothing to do with right triangles.
 

Related Threads on I need help on identities

  • Last Post
Replies
10
Views
816
  • Last Post
Replies
7
Views
4K
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
7
Views
1K
Replies
6
Views
6K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
5
Views
3K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
3
Views
3K
Replies
4
Views
963
Top