f（x）=根号下｛（5-x）/（x+1）｝∴｛（5-x）/（x+1）｝＞=0∴5-x＞=0x+1＞0（∵x+1在分母,∴≠0）x＜=5x＞-1∴A=(-1,5]g(x)=lg(-x^2+2x+m)m=3时-x^2+2x+3＞0 （x-3）（x+1）＜0∴...