Find the Reference Angle cos(120)

Problem

cos(120^∘)

Solution

1. Identify the quadrant in which the given angle θ=120^∘ lies. Since 90^∘<120^∘<180^∘ the angle is in Quadrant II.

2. Apply the formula for the reference angle θ^′ in Quadrant II, which is θ^′=180^∘−θ

3. Substitute the value of the angle into the formula.

θ^′=180^∘−120^∘

4. Subtract the values to find the reference angle.

θ^′=60^∘

Final Answer

Reference Angle of *120^∘=60^∘

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