Steps of Construction (i) Draw BC = 12 cm. (ii) Construct ÐCBY = 90°. (iii) From ray BY, cut-off line segment BD = 18 cm. (iv) Join CD. (v) Draw the perpendicular bisector of CD intersecting BD at A. (vi) Join AC to obtain the required △ABC. Justification Since A lies on the perpendicular bisector of CD. Therefore, AD = AC Now, BD = BA + AD ⇒ BD = AB + AC Hence, △ABC is the required triangle.