55. Because it is defined on R and is a odd function, it monotonically increases from 0 to infinity, so it is less than 0 at (0, 1) and less than 0 at (negative infinity,-1). Because it is odd function, the solution set is (negative infinity,-2) ∨ (-6746). ) you can find it.

56. Because the interval of single increment is from 3 to positive infinity, 2x+a=0 when x=3, and the function fx=2X+A when x increases, only in this way can the function be increased. Found one =-6