Question

find the value of cos 72 degree​

Answer 1

Step-by-step explanation:

refer to the attachment

Answer 2

Answer:

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°