Question

How to find the orthocentre of a obtuse angled triangle

Answer 1

Answer:

Same as for any triangle, the orthocentre is the point of intersection of the 3 altitudes, so just draw in two of the altitudes and get the point of intersection (you can also do the 3rd altitude as a check, of course!)

The thing that might cause confusion is that an altitude from a vertex might not go directly onto the opposite side.  That's fine... It's not actually the side of the triangle that matters, but the line that the side is a part of.  So just draw the whole line.

For instance, the altitude from A to BC is the line through A that is perpendicular to the line BC.  It doesn't matter if A is "above" BC or way over to the side!