Question

Which of the following does not equal cos340°?

-cos20°
cos20°
cos(-20°)

Answer 1

Only
`-cos20^o` is not equal to
`cos340^o`

Explanation:

Trigonometric values

The cosine of an angle can be read as the projection in the x-axis of one point in a unit circle centered in the origin. The angles can be expressed in degrees, from 0 to 360 to make a full rotation.

The value of
`340^o` is located
`20^o` before completing the first rotation. Therefore it can be also expressed as
`cos(-20^o)`. The cosine function is even, i.e. it complies to

`cosx=cos(-x)`

So
`cos(-20^o)=cos(20^o)`

Both quantities are positive, making the first option
`-cos20^o` incorrect

Summarizing only
`-cos20^o` is not equal to
`cos340^o`