# Trig function help

1. Jan 25, 2015

### Eric Manuel

thanks

Last edited: Jan 25, 2015
2. Jan 25, 2015

### Jimmy Johnson

Can you give the entire problem?

3. Jan 25, 2015

### Eric Manuel

all thats given is that

4. Jan 25, 2015

### MostlyHarmless

What is the question? What are you asked to find?

5. Jan 25, 2015

### Eric Manuel

what is =cos2x

6. Jan 25, 2015

### MostlyHarmless

What is x supposed to be? Is the given problem in terms of t? Are you trying to solve for t and then plug that value in for x?

7. Jan 25, 2015

### Eric Manuel

its basically asking you to use the double angle formula
but im not sure how to find those values

8. Jan 25, 2015

### Jimmy Johnson

If you're simply trying to find t, then use cot = 1/tan... If you have a value for t why do you need to use the double angle identities?

9. Jan 25, 2015

### Eric Manuel

to find what cos2t is ....

you can find what tan is from cot
then i drew a triangle and got the hypot to be sqrt(41)

but how do i do that math

formula for cos2t = cos^2(t) - sin^2(t)

10. Jan 25, 2015

### Jimmy Johnson

Are you forbidden from using a calculator?

11. Jan 25, 2015

### Eric Manuel

teacher said u can use it
but need to know how to do it without one for test

12. Jan 25, 2015

### Jimmy Johnson

Well that may have been useful information at the start...

you have cot = -5/4, find what tan is then recall tan = sin/cos ... or recall cot = cos/sin...

13. Jan 25, 2015

### Eric Manuel

well i worked it out and i believe i got the answer to be 9/41

14. Jan 25, 2015

### Jimmy Johnson

That's what I'm getting

15. Jan 25, 2015