I=∫π6π3dx1+√tanx......(i)I=∫π6π3dx1+√tan(π2−x)I=∫π6π3dx1+√cotxI=∫π6π3√tanxdx√tanx+1.......(ii)
Adding (i) and (ii)
2I=π6−π32I=−π6I=−π12