Find the Exact Value cos(-pi/4)

Problem

cos(−π/4)

Solution

1. Apply the even-odd identity for the cosine function, which states that cos(−θ)=cos(θ)

cos(−π/4)=cos(π/4)

2. Identify the reference angle value from the unit circle or a special right triangle (45−45−90.

π/4=45

3. Determine the exact value of the cosine of π/4

cos(π/4)=√(,2)/2

Final Answer

cos(−π/4)=√(,2)/2

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