1. Draw a line segment of base BC = 12 cm
2. Measure and draw ∠B = 90° and draw the ray BX
3. Using a compass measure AB+AC = 18 cm.
4. Considering B as a centre and draw an arc at the point be D on the ray BX
5. Join DC
6. Now draw the perpendicular bisector of the line CD and the intersection point is taken as A.
7. Now join AC
8. Hence, ABC is the required triangle.