Trigonometry

$$\displaystyle \left( \sin { \theta  } +\cos { \theta  }  \right) \left( 1-\sin { \theta  } \cos { \theta  }  \right) $$ can be written as :
If the angles of elevaton of the top of a tower from two points distance s and t $$\displaystyle \left ( s> t \right )$$ from its foot are $$\displaystyle 30^{0}$$ and $$\displaystyle 60^{0}$$ respectively then the height of the tower is