Question

The Unit Circle

What is cos(-30*)? Sketch a graph to help determine the answer

a. 0.50
b. 0.87
c. -1
d. 0

Please select the best answer from the choices provided

Answer 1

C. -1

Explanation:

I calculated it logically

Answer 2

The value of
`\(\cos(-30^\circ)\)` is the same as
`\(\cos(30^\circ)\)`, which equals
`\((√(3))/(2)\)` or approximately 0.87. Therefore, the correct answer is (b) 0.87.

The cosine function has periodicity of
`\(360^\circ\)`, which means
`\(\cos(\theta) = \cos(\theta \pm 360^\circ)\)`. Therefore,
`\(\cos(-30^\circ) = \cos(360^\circ - 30^\circ) = \cos(330^\circ)\)`.

Since
`\(\cos(330^\circ) = \cos(330^\circ - 360^\circ) = \cos(-30^\circ)\)`, the value is the same as
`\(\cos(-30^\circ)\)`.

Now, recall that
`\(\cos(-\theta) = \cos(\theta)\)`. Therefore,
`\(\cos(-30^\circ) = \cos(30^\circ)\)`.

The cosine of
`\(30^\circ\)` is
`\((√(3))/(2)\)` or approximately 0.87.

So, the correct answer is:

b. 0.87