What is the value of cos(216) ?

The value of cos(216) is -(sqrt(5)+1)/4

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cos(216)

cos (21 6^{\circ})

- \frac{5 + 1}{4}

Solution steps

cos (21 6^{\circ})

Rewrite using trig identities:

cos (14 4^{\circ})

= cos (14 4^{\circ})

Rewrite using trig identities:

- cos (3 6^{\circ})

= - cos (3 6^{\circ})

Rewrite using trig identities:

cos (3 6^{\circ}) = \frac{5 + 1}{4}

= - \frac{5 + 1}{4}

10 \cdot sin (2 0^{\circ})

4 sin (1 0^{\circ})

cos (arcsin (\frac{- 3}{2}))

sin (4 5^{\circ}) + cos (4 5^{\circ}) + tan (4 5^{\circ})

cos (\frac{5}{4})