1.1> f:=expand((x+1)*(x+0)*(x-1)*(x-2));

                            4      3    2
                      f := x  - 2 x  - x  + 2 x

1.2> diff(f,x);

                           3      2
                        4 x  - 6 x  - 2 x + 2

1.3> plot(f,x=-2..3);

1.4> d:=f/diff(f,x);

                            4      3    2
                           x  - 2 x  - x  + 2 x
                      d := ---------------------
                              3      2
                           4 x  - 6 x  - 2 x + 2

> subs(x=3,d);

                                  12
                                  --
                                  25

 
1.5> I'm not using Excel, so...

1.6> I'm not using Excel, but at a guess, x=2?

1.7> x=-1: x1<-1
     x=0: -0.1<x1<0.1
     x=1: 0.9<x1<1.1
     x=2: x1>2

1.8> You won't find anything because the gradient there is 0. ;-)

1.9.1> done

1.9.2> done

2.1> ok...

2.2> assumed

3.1> see 3.3

3.2> see 3.3

3.3> see s5q3-3.c

end.