Construct an equilateral triangle whose altitude is 4.5 cm.

Steps of construction:

(i) Draw any line l and take a point D on it.

(ii) Construct a perpendicular to l at D and cut AD = 4.5 cm.

(iii) Draw the angle of 30° at on either side of AD to meet the line l at B and C.

(iv) ΔABC is the required equilateral triangle.