## tammyhawatmeh 2 years ago cos θ = − root2 /2

1. baldymcgee6

how can you get rid of the cosine?

2. tammyhawatmeh

arc cos?

3. baldymcgee6

yep

4. baldymcgee6

do you know the unit circle?

5. tammyhawatmeh

yup

6. baldymcgee6

okay, so where is cos(θ) = -sqrt(2/2) ?

7. tammyhawatmeh

3pi/4

8. baldymcgee6

Yes.. correct.

9. hartnn

what about 5pi/4 ?

10. hartnn

now do u need general solution or within the range 0 to 2pi ?

11. tammyhawatmeh

these are the directionsSolve the given equation. (Enter your answers as a comma-separated list. Let k be any integer. Round terms to two decimal places where appropriate.)

12. hartnn

means genearalized solution, can u generalize this ?

13. tammyhawatmeh

5pi/4 ,-5pi/4,3pi/4,-3pi/4

14. baldymcgee6

There is an infinite amount of solutions, you need to write it in a way to GENERALIZE the solution.

15. hartnn

so let me generalize it. cos function is periodic with 2pi. so values repeat after every 2pi*k here, $$\theta =\pm(3\pi/4+2\pi k),\pm(5\pi/4+2\pi k)$$

16. tammyhawatmeh

ohh i see but why do u add the 2pik at the end ? because it is a periodic function?

17. hartnn

yes, as i said cos function is periodic with 2pi. so if a is solution, so is a+2pi, a-2pi,a+4pi,a-4pi, and so on

18. tammyhawatmeh

ohh i see i missed this whole lesson on this section and i dont know any of it