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(52921) (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(20065) (Show Source):
You can put this solution on YOUR website!
If
,
evaluate

Edwin