Question

Cos square pi by 8 + cos sq. 3pi by 8 + cos sq. 5pi by 8 + cos sq 7 pi by 8 = 2

Answer 1

cos²π/8 + cos²3π/8 + cos²(π - 3π/8) + cos²(π - π/8)

⇒ 2cos²π/8 + 2cos²3π/8

⇒ 2{cos²π/8 + cos²(π/2 - π/8)

⇒ 2{ cos²π/8 + sin²π/8 }

⇒ 2{1} = 2

Answer 2

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