2.？ 18? (What is the symmetry axis of the function? x=6？ There are three roots, so one of them must be 6, and the sum of the other two is 12)

3.？ 0? (from F(X)=a+(2/x+b)? Find F- 1(x) and get a=-b)

4.？ Maximum value: 2 Minimum value: 0. (about x deducing y? y'=(-6x^2+54)/(9+x^2)^2？ Make y'=0? Have to? X=3 and -3)

5.？ (Y = 5x 2+ 1) The image is symmetrical about y, and the minimum value is 1, which is a parabola with an upward opening.

6? . As shown in the figure