Evaluate cos(-90 degrees )

Problem

cos(−90)

Solution

1. Identify the property of the cosine function for negative angles. Cosine is an even function, which means cos(−θ)=cos(θ)

2. Apply the property to the given expression to rewrite it with a positive angle.

cos(−90)=cos(90)

3. Determine the value of the cosine function at 90 using the unit circle or trigonometric tables. At 90 the coordinates on the unit circle are (0,1)

4. Recall that the cosine of an angle corresponds to the xcoordinate of the point on the unit circle.

cos(90)=0

Final Answer

cos(−90)=0

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