For any given positive masses it is proved that the variational minimization solutions of the 3-body problem in ii3 or A? are precisely the planar equilateral triangle circular solutions found by J. Lagrange in 1772, and that the variational minimization solutions of the circular restricted 3-body problem in IFF or ?t2 are also planar equilateral triangle circular solutions. Keywords : 3-body problem, d t i o n a l minimhatinn, equilateral triangle drcnlar solution.THE classical N-body problem in the celestial mechanics concerns the motion of N point masses governed by the universal gravitation law. The motion q = ( q , ( t ) , , qfi( t ) ) satisfies the following system:where qi E lRK with K = 3 or 2 being the position, mi is the mass of the i-th particle for i = 1 , ... , N respectively, and -U( g ) is the potential function given by and U,, denotes the gradient of U with respect to q i . By K > 0 we denote the universal gravitation constant. After Rabinowitz' pioneering work['] in 1978. a great amount of contributions to periodic solutions of the N-body problems as well as restricted N-body problems has been made via variational minimization method on r-periodic function spaces. Two beautiful survey works are refs. [ 2 1 and [ 3 1 ( cf. also refs [4-81 and references therein) . Many mathematicians work on r/2-antiperiodic function paces, where a function q = q ( t ) is called r/2-antiperiodic, if q ( t + r / 2 ) = -q ( t ) for all t E Z . Via the variational minimization methods, the existence of non-collision periodic solutions was proved for the 2-body problem by Degiovanni and Giannoni in ref. [ 7 ] of 1989, and for the 3-body problem in Yt3 by Serra and Terracini in ref. [8] of 1992. Note that ref. [ 81 depends on the famous and heavy work of Sundman at the begrnning of this century[91 and does not apply to the 3-body problem in 3'.