Multiple Choice
On the unit circle, which trigonometric functions are undefined when ?
3. Unit Circle
Trigonometric Functions on the Unit Circle
Multiple Choice
Which expression is equivalent to ?
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Verified step by step guidance1
Recall that the cosine function for angles greater than 90° can be evaluated using the reference angle and the unit circle properties.
Identify the reference angle for 120° by subtracting 120° from 180°, which gives \(180^\circ - 120^\circ = 60^\circ\).
Since 120° lies in the second quadrant where cosine values are negative, the cosine of 120° is the negative cosine of its reference angle 60°.
Write the expression for \(\cos 120^\circ\) as \(-\cos 60^\circ\).
Use the known value \(\cos 60^\circ = \frac{1}{2}\) to express \(\cos 120^\circ\) as \(-\frac{1}{2}\).
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