Steps of Construction
(i) Draw a line XY.
(ii) Construct perpendicular PD at any point D on the line XY.
(iii) From point D, cut-off line segment AD = 6 cm.
(iv) Construct ∠BAD = ∠CAD = 30°. Then ABC is the required triangle.
Justification
As ∠A = ∠BAD + ∠CAD = 30 °+ 30° = 60° and AD perpendicular BC therefore, △ABC is an equilateral triangle with altitude AD = 6 cm.