Trigonometry Examples

\cos^{2} (\frac{2 π}{5}) - \sin^{2} (\frac{2 π}{5})

$\cos^{2} (\frac{2 π}{5}) - \sin^{2} (\frac{2 π}{5})$

Step 1

Apply the cosine double-angle identity.

\cos (2 \frac{2 π}{5})

$\cos (2 \frac{2 π}{5})$

Step 2

Multiply

2 \frac{2 π}{5}

$2 \frac{2 π}{5}$ .

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Step 2.1

Combine

2

$2$ and

\frac{2 π}{5}

$\frac{2 π}{5}$ .

\cos (\frac{2 (2 π)}{5})

$\cos (\frac{2 (2 π)}{5})$

Step 2.2

Multiply

2

$2$ by

2

$2$ .

\cos (\frac{4 π}{5})

$\cos (\frac{4 π}{5})$

\cos (\frac{4 π}{5})

$\cos (\frac{4 π}{5})$

Step 3

The result can be shown in multiple forms.

Exact Form:

\cos (\frac{4 π}{5})

$\cos (\frac{4 π}{5})$

Decimal Form:

- 0.80901699 \dots

$- 0.80901699 \dots$