Construct an isosceles triangle whose altitude is 5 cm and whose vertex angle is 80°.

In an isosceles triangle, the altitude dropped from the vertex is also its angle bisector using this property we are going to construct the triangle

Step1: construct a line segment XY and consider a point M on it and using protractor draw a line perpendicular to XY passing through M

Step2: as the altitude is 5 cm mark point A above M at 5 cm

Step3: now using protractor draw lines at angles at 40° to the left of A and 40° to the right of A and mark the intersection points with line XY as B and C respectively thus required ΔABC is ready