how to determine the possition of orthocentre of triangle?i.e inside,outside or on the tringle.

The orthocenter is not always inside the triangle. If the triangle is obtuse , it will be outside. To make this happen the altitude lines have to be extended so they cross. Adjust the figure above and create a triangle where the orthocenter is outside the triangle. Follow each line and convince yourself that the three altitudes, when extended the right way, do in fact intersect at the orthocenter.