Asked by Quinn

Solve for θ in the equation cos θ = 0.778 when 180º < θ < 360º. Round your answer to the nearest tenth of a degree.
Answered by Reiny
180º < θ < 360º and cosθ is positive means that θ lies in quadrant IV

On your calculator enter:
2ndF
cos
.778
=
and you should get and acute angle.
that would be the angle in standard position, so
θ = 360- angle = ..... to the nearest tenth.

check by taking cos(of your angle)

let me know what you get.
Answered by Quinn
I get 38.9 and then subtracting it from 360 gets 321.1 which isn't the correct answer, apparently.
Answered by Reiny
That is the answer I got,

and when I find cos 321.1 , I get .778243, which matches the given
considering that we rounded to one decimal.

Our answer is correct.
Answered by Quinn
Well, I've tried every possible variation for it, but it won't say it's correct. I'll ask my teacher. Thank you so much!
Answered by R_scott
just a thought ... are you using the degree symbol in your answer?

321.1º

alt-167

radians is the default I think ... degrees must be specified

Answered by Reiny
The domain was definitely given in degrees:
180º < θ < 360º
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