What is the value of 1-2sin^2((3pi)/5) ?

The value of 1-2sin^2((3pi)/5) is -(sqrt(5)+1)/4

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1-2sin^2((3pi)/5)

1 - 2 sin^{2} (\frac{3 π}{5})

- \frac{5 + 1}{4}

Solution steps

1 - 2 sin^{2} (\frac{3 π}{5})

Rewrite using trig identities:

sin (\frac{3 π}{5}) = sin (\frac{2 π}{5})

= 1 - 2 sin^{2} (\frac{2 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 (2 π \cdot 2)

arccos (\frac{4}{32})

(- 8.5 cos (4 0^{\circ})) - (22 sin (2 0^{\circ}))

1 + cos (\frac{2 π}{3})

csc (1 2^{\circ})

What is the value of 1-2sin^2((3pi)/5) ?
The value of 1-2sin^2((3pi)/5) is -(sqrt(5)+1)/4