What is the value of cos(-(4pi)/5) ?

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

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cos(-(4pi)/5)

cos (- \frac{4 π}{5})

- \frac{5 + 1}{4}

Solution steps

cos (- \frac{4 π}{5})

Use the following property:

cos (- x) = cos (x)

cos (- \frac{4 π}{5}) = 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}

30 cos (4 7^{\circ})

cot (10 0^{\circ})

sin^{2} (\frac{5 π}{6})

arccsc (\frac{3}{2})

sin (arcsin (\frac{1}{2}) - arccos (0))

What is the value of cos(-(4pi)/5) ?
The value of cos(-(4pi)/5) is -(sqrt(5)+1)/4