Simplify cos(2arccos(2/5))

$\cos (2 \arccos (\frac{2}{5}))$

Evaluate $\arccos (\frac{2}{5})$ .

$\cos (2 \cdot 1.15927948)$

Multiply $2$ by $1.15927948$ .

$\cos (2.31855896)$

The result can be shown in multiple forms.

Exact Form:

$\cos (2 \arccos (\frac{2}{5}))$

Decimal Form:

$- 0.68000000 \dots$

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