Any obtuse triangle will necessarily have two angles that are not obtuse (assuming Euclidean geometry). Regardless, to draw any altitude of triangle, you need the triangle in question, and a method of drawing or detecting a particular angular measure.
What you're going to need to do is draw a line that is both perpendicular to the edge furthest from a given angle of a triangle, straight up to the corner in question. In the case of a obtuse triangle, this will usually result in two of the altitudes being outside the triangle: This is normal.
In short, do the following:
You'll need
[1] a copy of the triangle.
[2] a straight edge
[3] a way to draw a line 90 degrees from a straight line.
1. Take your copy of the triangle and lay the straight edge along one of the sides.
2. Take your [3] tool and draw a straight line, 90 degrees from this edge all the way up to the other point on the triangle that doesn't touch this edge.
3. Repeat for all three corners.
What you're going to need to do is draw a line that is both perpendicular to the edge furthest from a given angle of a triangle, straight up to the corner in question. In the case of a obtuse triangle, this will usually result in two of the altitudes being outside the triangle: This is normal.
In short, do the following:
You'll need
[1] a copy of the triangle.
[2] a straight edge
[3] a way to draw a line 90 degrees from a straight line.
1. Take your copy of the triangle and lay the straight edge along one of the sides.
2. Take your [3] tool and draw a straight line, 90 degrees from this edge all the way up to the other point on the triangle that doesn't touch this edge.
3. Repeat for all three corners.