SOLUTION: If sin^2 (𝛑/9) + sin^2 (2𝛑/9) + sin^2 (3𝛑/9) + sin^2 (4𝛑/9) = 9/4, Evaluate cos^2 (𝛑/9) + cos^2 (2𝛑/9) + cos^2 (3𝛑/9) + cos^2 (4𝛑/9)

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Question 1152666: If sin^2 (𝛑/9) + sin^2 (2𝛑/9) + sin^2 (3𝛑/9) + sin^2 (4𝛑/9) = 9/4,
Evaluate cos^2 (𝛑/9) + cos^2 (2𝛑/9) + cos^2 (3𝛑/9) + cos^2 (4𝛑/9)
Found 2 solutions by ikleyn, Edwin McCravy:
Answer by ikleyn(52925)   (Show Source): You can put this solution on YOUR website!
.

cos^2 (𝛑/9)         + cos^2 (2𝛑/9)       + cos^2 (3𝛑/9)       + cos^2 (4𝛑/9) = 


= (1 - sin^2 (𝛑/9)) + (1 - sin^2 (2𝛑/9)) + (1 - sin^2 (3𝛑/9)) + (1 - sin^2 (4𝛑/9)) = 


= 4 - (sin^2 (𝛑/9) + sin^2 (2𝛑/9) + sin^2 (3𝛑/9) + sin^2 (4𝛑/9)) =  =  = .    ANSWER


Answer by Edwin McCravy(20066)   (Show Source): You can put this solution on YOUR website!
If
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evaluate 
















Edwin
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