## anonymous one year ago Is this correct? Solve the equation on the interval of $$0\geq \theta < 2\pi$$ $$2cos \theta + 3 = 2$$ $$2 cos \theta = 2-3$$ $$2 cos \theta = -1$$ $$\frac{2 cos \theta}{2} = \frac{-1}{2}$$ $$cos \theta = \frac{-1}{2}$$ This was on my midterm and I made an A on it but this one I got wrong but this looks correct? What did I do wrong?

1. anonymous

Solve the equation on the interval of $$0\geq \theta < 2\pi$$ $\huge 2\cos \theta + 3 = 2$ $\huge 2 \cos \theta = 2-3$ $\huge 2 \cos \theta = -1$ $\huge \frac{2 \cos \theta}{2} = \frac{-1}{2}$ $\huge \cos \theta = -\frac{1}{2}$

2. Curry

wait how many answers did you provide? there are two answers.

3. anonymous

One sec it should be $$\huge 0\leq \theta < 2\pi$$

4. anonymous

I provided one

5. anonymous

but if we work out the equation, like I did, it comes to what I have

6. TheSmartOne

You need to solve for $$\sf\theta$$

7. anonymous

Ok so he wanted the angle

8. TheSmartOne

Yes, and you should get 2 answers for the angle

9. anonymous

Yes I get two. I was thinking he just wanted us to do it like that because some of our homework does it like I just did it.

10. TheSmartOne

What 2 angles did you get? :)

11. DanJS

cos(a) = x on the unit circle with radius 1... picture that thing

12. anonymous

I got 120 and 240 degrees. or 2pi/3 and 4pi/3

13. TheSmartOne

|dw:1435870657418:dw|

14. TheSmartOne

Correct :)

15. anonymous

Yep that is it :-) Just a silly mistake on my part :-( oh well lol

16. anonymous

Got the hardest one right because I put the angle lol

17. TheSmartOne

If they didn't have the restrictions on the value of $$\sf\theta$$ then the answer would be: $$\sf\Large \theta=\frac{2\pi}{3}\pm2\pi n$$ $$\sf\Large \theta=\frac{4\pi}{3}\pm2\pi n$$

18. anonymous

Funny, I made the same mistake on two but for some reason, on the hardest one I put the angle for that one but not the other two.... . DUFF what was I thinking lol

19. anonymous

Anyways... I still have an A in the class and I made an A on the midterm so I am happy :-)

20. TheSmartOne

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