Question

Which of the following does not equal cos340°? -cos20° cos20° cos(-20°)

Answer 1

Answer:

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

Step-by-step 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 $cos340^o$