Steps of construction:
1. Draw a line segment AB = 5 cm. Construct a right angle SAB at point A.
2. Draw an arc of radius 12 cm with B as its centre to intersect SA at C.
3. Join BC to obtain ABC.
4. Draw a ray AX making an acute angle with AB, opposite to vertex C.
5. Locate 3 points, A1, A2, A3 on line segment AX such that AA1 = A1A2 = A2A3.
6. Join A3B.
7. Draw a line through A2 parallel to A3B intersecting AB at B’.
8. Through B’, draw a line parallel to BC intersecting AC at C’.
9. Triangle AB’C’ is the required triangle.