1. An altitude of a triangle is a line segment from a vertex perpendicular to the opposite side.

2. The point of concurrence of the altitudes of a triangle is called its orthocentre.

3. In a right triangle, the orthocentre is at vertex of the right angle.

4. The altitudes drawn on equal sides of an isosceles triangle are equal.

5. The three altitudes of an equilateral triangle are equal.