Question

How to construct an orthocenter of a triangle???

Answer 1

The altitude of a triangle is a line which passes through a vertex of the triangle and is perpendicular to the opposite side. There are therefore three altitudes possible, one from each vertex.

It turns out that all three altitudes always intersect at the same point - the so-called orthocenter of the triangle.

Answer 2

Draw the triangle.  Then draw the perpendicular from two vertices onto the opposite sides.  The point of intersection is the Orthocenter.

Tow draw the perpendicular use the geometric tool in the box.