Answer:
cosβ = -1/2
Explanation:
Since cos2β = 3/4 and β is in quadrant III, the value of cosβ must be negative. We can find the exact value of cosβ by using the identity cos2β = 2cos^2β - 1. Substituting 3/4 for cos2β and solving for cosβ, we get:
3/4 = 2cos^2β - 1
cos^2β = 1/4
cosβ = 1/2 or -1/2
Since cosβ is negative in quadrant III, the value of cosβ is -1/2. Thus, the answer is cosβ = -1/2.
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