An [i]altitude[/i] of a triangle is a line that passes through a vertex of the triangle and is perpendicular to the opposite side. Therefore, [b]every triangle has three altitudes[/b], which all meet at a single point. This point is a candidate for the center of the triangle and is called the [b]orthocentre[/b].[br][br]a) Draw an arbitrary triangle in GeoGebra and use the appropriate tools to find its orthocentre in a reasoned manner.[br][br]b) With the construction already made, move the initial triangle and observe what happens to its orthocentre. Based on what you observe, propose a criterion (a rule) to determine, without drawing it, whether the orthocentre of a triangle will lie inside, outside, or on one of its sides (if possible).