It is known that the odd function f (x) defined on R is a decreasing function. If X1 + x2 < 0, X2 + X3 < 0, X3 + X1 < 0, then the value of F (x1) + F (x2) + F (x3)______ ．

It is known that the odd function f (x) defined on R is a decreasing function. If X1 + x2 < 0, X2 + X3 < 0, X3 + X1 < 0, then the value of F (x1) + F (x2) + F (x3)______ ．

∵ X1 + x2 ＜ 0, X2 + x3 ＜ 0, X3 + x1 ＜ 0, ∵ x1 ＜ - X2, X2 ＜ - X3, x3 ＜ - x1, and f (x) is a monotonically decreasing odd function defined on R, ∵ f (x1) > F (- x2) = - F (x2), f (x2) > F (- x3) = - f (x3), f (x3) > F (- x1) = - f (x1), ∵ f (x1) + F (x2) ＞ 0, f (x3) + F (x1) ＞ 0, ∵ the three formulas are summed up and sorted out（ X1) + F (x2) + F (x3) > 0, so the answer is: greater than 0