2 2x2+ 3 3,③ 恒等式 0=0.④ 取x3为自由变量,则 C+4 c+3 3 令x3=c,则X 31 2 3 4 2 3 4 4 2 4, 0, 3, 0 0. x x x x x x x x  + − + =   − + =  = −    = 取 x3 为自由变量，则 1 3 2 3 4 4, 3, 3. x x x x x  = +   = +   = − 令 x3 = c ，则 1 2 3 4 4 3 3 x c x c X x c x     +     +     = =             − 恒等式 1 4 1 3 . 1 0 0 3 c             = +             − ① ② ③ ④