Draw a straight line across the paper. Line up the bottom of the protractor with the line. Mark the 90-degree point above the line.
Choose one of the altitudes. Draw a line straight up so that it lies perpendicular to the bottom line and measures the length of the altitude. The bottom line is the first side of your triangle.
Lay the ruler on top of the protractor so that the measure edge lines up with the center point of the protractor and the 90-degree mark at the top of the curve.
Line up the bottom of the protractor with the first horizontal line to the left of center. Mark the spot for reference.
Pivot the protractor/ruler combination counterclockwise until the ruler crosses the first altitude. Continue to pivot the tools until the ruler crosses the bottom horizontal line at the length of the second altitude. Mark the spot on the line. Mark both corners of the base of the protractor. Mark the center point of the protractor. Remove the tools.
Draw a line connecting the two marks from the base of the protractor. Draw a second line connecting the mark on the line and the mark on the center of the protractor. The first line is a side of the triangle and the second is the altitude.
Measure the angle between the first and second sides of the triangle. This is the angle between the bottom and left-hand lines. Lay the protractor so that the bottom line is straight across the base of the protractor. Look at the numbers along the upper curve and record the number that the second, left-hand line crosses. Divide the number by two and mark the center of the angle on the paper. Call this the center point.
Lay the ruler so that it bisects the angle. Measure the final altitude distance from the angle. Draw a line between the angle and the center point that equals the final altitude.
Lay the protractor so that the final altitude is at the 90-degree point on the protractor and the bottom is at the end of the measured line opposite the angle. Draw a line that crosses the other two sides.
Erase any lines that extend beyond the boundaries of the triangle.