What is the angle between two vector forces of equal magnitude such that the resultant is one third as much as either of the original forcse?

Hi Praveen,Let the force vectors be A and B.Then |A| =|B| ….......................(1) {Given}And also,|A +B| = |A|Squaring both sides,|A|^2 + |B|^2 + 2.A.B = |A|^2|B|^2 + 2A.B = 0..........................(2)Now Angle between the tqo vectors is:cos@ = A.B/|A|.|B| = A.B/|B|^2 (Given = |A| =|B|). From eqn. (2)A.B/|B|^2 = -1/2 = cos@@ = 120 degree.