What is the value of cos(0.4pi) ?

The value of cos(0.4pi) is (sqrt(2)sqrt(3-\sqrt{5)})/4

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cos(0.4pi)

cos (0.4 π)

\frac{2 3 - 5}{4}

Solution steps

cos (0.4 π)

= cos (\frac{2}{5} π)

Simplify:

\frac{2}{5} π = \frac{2 π}{5}

= cos (\frac{2 π}{5})

Rewrite using trig identities:

sin (\frac{π}{10})

= sin (\frac{π}{10})

Rewrite using trig identities:

\frac{1 - cos ( \frac{π}{5} )}{2}

= \frac{1 - cos ( \frac{π}{5} )}{2}

Rewrite using trig identities:

cos (\frac{π}{5}) = \frac{5 + 1}{4}

= \frac{1 - \frac{5 + 1}{4}}{2}

Simplify

\frac{1 - \frac{5 + 1}{4}}{2} : \frac{2 3 - 5}{4}

= \frac{2 3 - 5}{4}

tan (\frac{9}{7})

cot^{2} (\frac{π}{4})

cos (3 0^{\circ}) - sin (3 0^{\circ})

sin (0.72)

cos (2 4^{\circ}) sin (2 4^{\circ})

What is the value of cos(0.4pi) ?
The value of cos(0.4pi) is (sqrt(2)sqrt(3-\sqrt{5)})/4