What is the value of cos(1.2pi) ?

The value of cos(1.2pi) is -(sqrt(5)+1)/4

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cos(1.2pi)

cos (1.2 π)

- \frac{5 + 1}{4}

Solution steps

cos (1.2 π)

= cos (\frac{6}{5} π)

Simplify:

\frac{6}{5} π = \frac{6 π}{5}

= cos (\frac{6 π}{5})

Rewrite using trig identities:

cos (\frac{4 π}{5})

= cos (\frac{4 π}{5})

Rewrite using trig identities:

- cos (\frac{π}{5})

= - cos (\frac{π}{5})

Rewrite using trig identities:

cos (\frac{π}{5}) = \frac{5 + 1}{4}

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

sin (4 5^{\circ}) cos (33 0^{\circ}) + sin (15 0^{\circ}) cos (40 5^{\circ}) cot (21 0^{\circ})

sin (19 5^{\circ}) - sin (7 5^{\circ})

40 π [0.6 + (\frac{sin ( 8 π \cdot 0.6 )}{8 π})]

50 cos (2 0^{\circ})

tan (arccos (\frac{6}{7}))