The value of  tan9o−tan27o−tan63o+tan81o is _____.

The given expression is tan9° - tan27° - tan63° + tan81°.

We know that tan(90° - θ) = cot θ. So we can write the expression as follows:

tan9° - tan27° - tan(90° - 27°) + tan(90° - 9°)

This simplifies to:

tan9° - tan27° - cot27° + cot9°

We also know that tan θ - cot θ = 0. So the expression simplifies to:

0 - 0 = 0

So, the value of tan9° - tan27° - tan63° + tan81° is 0.