Construct a triangle ABC in which AB = 3.5 cm, AC = 4 cm and length of the perpendicular from A to BC is 3 cm.

Step1: Construct a line XY and take a point M on it and draw a ray MZ perpendicular to XY as shown

Step2: as the altitude is 3 cm mark point A above XY on MZ at 3 cm from point M using a scale or a compass

Step3: take distance of 3.5 cm in compass keep the needle of the compass on point A and mark an arc intersecting XY at B. join AB

Step4: take distance 4 cm in compass keep the needle of the compass on point A and mark an arc intersecting XY at C. join AC and ΔABC is ready