Find the Exact Value cos((2n+1)*90 degrees )

$\cos ((2 n + 1) \cdot 90 °)$

Apply the distributive property.

$\cos (2 n \cdot 90 ° + 1 \cdot 90 °)$

Multiply.

Multiply $90 °$ by $2$ .

$\cos (180 n + 1 \cdot 90 °)$

Multiply $90 °$ by $1$ .

$\cos (180 n + 90 °)$