Step-by-step explanation:
refer to the attachment
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kirad0fo
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The value of cos 72 degrees is 0.3090169. . .. Cos 72 degrees in radians is written as cos (72° × π/180°), i.e., cos (2π/5) or cos (1.256637. . .).
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We can use trigonometric identities to represent cos 72° as,
-cos(180° - 72°) = -cos 108°
-cos(180° + 72°) = -cos 252°
sin(90° + 72°) = sin 162°
sin(90° - 72°) = sin 18°
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benlbm5
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