Show an example of how to evaluate a trigonometric function using reference angle (without a calculator/ you may use left hand rule or unit circle)

Explanation:

An example is as follows;

Using reference angle, evaluate

Solution:

We have:

150 degrees is in the second quadrant, and it makes 30 degrees (i.e. 180 - 150) with the x-axis.

This implies that, cos(150) has the same magnitude as cos(30);

The only difference in the values is the sign; because

30 degrees is in the first quadrant where all functions are positive150 degrees is in the third quadrant where all cosine is negative

So, we have:

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