Construct a triangle of sides 4 cm, 5cm and 6cm and then a triangle similar to it whose sides are 2/3 of the corresponding sides of the first triangle.
Let the triangle with sides 4 cm,5 cm and 6 cm be ΔABC
Step1: construct segment AC of 6 cm
Step2: take distance 4 cm in compass keep the needle of the compass on point A and mark an arc above AC
Step3: take distance 5 cm in compass keep the needle of the compass on point C and mark an arc intersecting the arc drawn in step2. Mark intersection point as B join AB and AC
Step4: draw a ray from point A below AC at any angle
Step5: take any distance in compass and keeping the needle of the compass on point A cut an arc on ray constructed in step4 and name that point X1. Keeping the distance in compass same keep the needle of the compass on point X1 and cut an arc on the same ray and mark that point as X2. Draw 3 such parts (greater of 2 and 3 in 2/3), i.e. by repeating this process mark points upto X3
Step6: join X3 and C and from X2 (because X2 is the second point 2 being smaller in 2/3) construct line parallel to X3C and mark the intersection point with AC as D
Step7: construct line parallel to BC from point D and mark the intersection point with AB as E thus ΔADE ~ ΔACB is ready