An acute triangle has all of its angles less than 90 . The orthocentre of a triangle is the intersection point of its altitudes.
Points are collinear iff they lie on a straight line.
Explain your answer. Prove that at least two of the numbers are equal. Given 21 points on the circumference of a circle, prove that at least 100 of the arcs determined by pairs of these points subtend an angle not exceeding 120 at the centre. Prove that the points M, N and P are collinear.