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: -0.12 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.