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10.2

Part of VII Soros Olympiad 2000 - 01

Problems(1)

cos of a,b,(a+b) rational if sines rational (VII Soros Olympiad 2000-01 R1 10.2)

Source:

7/28/2021
Let aa and b b be acute corners. Prove that if sin⁡a\sin a, sin⁡b\sin b, and sin⁡(a+b)\sin (a + b) are rational numbers, then cos⁡a\cos a, cos⁡b\cos b, and cos⁡(a+b)\cos (a + b) are also rational numbers.
trigonometryalgebrarational