2 cos 2 5 -1 8 Write the following expression as the sine, cosine, or tangent of a double angle. Sele in the answer box to complete your choice. (Simplify your answer. Type an exact answer, using it as needed. Use integers or fra expression.) 5 2 OA. 2 cos - 1 = cos 8 5 2 OB. 2 cos - 1 = sin 8 5 2 - 1 = tan 8 OC. 2 cos The exact value of the given expression is