Find the Exact Value cos(pi/9)^2-sin(pi/9)^2

$\cos^{2} (\frac{π}{9}) - \sin^{2} (\frac{π}{9})$

Apply the cosine double-angle identity.

$\cos (2 \frac{π}{9})$

Combine $2$ and $\frac{π}{9}$ .

$\cos (\frac{2 π}{9})$

The result can be shown in multiple forms.

Exact Form:

$\cos (\frac{2 π}{9})$

Decimal Form:

$0.76604444 \dots$