Michael A. answered • 02/12/17

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1. sin 450° = sin 90° if we subtract one revolution, or 360°, to find the co-terminal angle. We know that sin 90° = 1

2. cos (-780°) = cos (-60°) when we add two revolutions, or 720°. In general:

cos (-x) = cos x, so cos (-60°) = cos 60° = 1/2

3. tan (37π/6) = tan (π/6) when we subtract three revolutions, or 36π/6 radians. Remember 2π radians = one revolution.

tan (π/6) = 1/√3 = √3/3