Identify the base of the triangle
Measure the perpendicular distance from the opposite vertex to the base
Draw a perpendicular line from the vertex to the base if needed
Use the formula ( A = frac{1}{2}bh )
Solve for altitude with ( h = frac{2A}{b} )
If the triangle is right, use the leg perpendicular to the chosen base as the altitude
If the triangle is isosceles, split it into two right triangles and use the perpendicular bisector
If the triangle is equilateral, use ( h = frac{sqrt{3}}{2}s )