1.  Draw line PE=4cm using scale
2.  At point P , taking P as center draw arc of radius 3cm
3.  Draw a arc of radius  5cm taking E as center.Let both arc intersect at point N. 4.  Join line EN and NP  using scale .
5.  If the circles are drawn they will intersect at another point bellow line PE.You will get congruent triangle. This is true for all triangles.