Write the following expression as the sine, cosine, or tangent of a double-angle. Then find the exact value...

Write the following expression as the sine, cosine, or tangent of a double-angle. Then find the exact value of the expression.
2 tan π / (1 - tan^2 π)
What is the given expression equal to? Select the correct choice below and fill in the answer box within your choice. (Simplify your answer. Type an exact answer, using pi as needed. Use integers or decimals for any numbers in the expression.)
A. 2 tan π / (1 - tan^2 π) = cos [ ]
B. 2 tan π / (1 - tan^2 π) = sin [ ]
C. 2 tan π / (1 - tan^2 π) = tan [ ]