Read the proof. A 2-column table with 3 rows. Column 1 is labeled Step with entries tangent (2 x) = tangent (x + x), question mark, = StartFraction 2 (x) Over 1 minus tangent squared (x) EndFraction. Column 2 is labeled Reason with entries Addition, question mark, simplify.

What is the missing step and reason?

Equals StartFraction tangent (x) + tangent (x) Over 1 minus tangent (x) tangent (x) EndFraction tangent double angle identity
Equals StartFraction tangent (x) + tangent (x) Over 1 minus tangent (x) tangent (x) EndFraction tangent sum identity
Equals StartFraction tangent (x) + tangent (x) Over 1 + tangent (x) tangent (x) EndFraction tangent double angle identity
Equals StartFraction tangent (x) + tangent (x) Over 1 + tangent (x) tangent (x) EndFraction tangent sum identity