(%i2) f(x):=-k*x^3+3*k^2*x^2;
3 2 2
(%o2) f(x) := (- k) x + 3 k x
(%i3) df(x):=diff(f(x),x)$ df(x);
2 2
(%o3) 6 k x - 3 k x
(%i4) df(k)=3;
3
(%o4) 8 k = 3
whats this? should have
(%i5) 6*k^2*x-3*k*x^2 = 3, x=k;
(%o5) 3*k^3 = 3
using define all works fine....
Gru? HW