Question

For what x-value(s) does cos(x) = -1?
Answers
-270°, -90°, 90°, and 270°
-270°, -90°, 0°, 90°, and 270°
-180° and 180°
-360°, 0° and 360

Answer 1

it would be the last one?

Answer 2

or the third?

Answer 3

Remember that on a unit circle, the cosine of an angle is equal to the x value. So, you're looking for the place where the x coordinate of a point on the unit circle is -1. This will only happen at an angle of 180 degrees, which is equivalent to an angle of -180 degrees.

Answer 4

so it wouldn't be -360 ?

Answer 5

because if cosx = 1 it would be 0 360 and -360

Answer 6

For 0 360 and -360, cosine is equal to positive 1, yes. This question said negative 1 though.

Answer 7

yes it negative so it would be 180 ?

Answer 8

I thought I would have to flip it around

Answer 9

Right. 180 or -180. They're the same angle.

Answer 10

okay so then it would be third one?

Answer 11

thank you!

Answer 12

Yes, exactly. You're welcome, glad I could help

Answer 13

:)