   My calculus is rusty...
  Let f1(x), f2(x), ..., fn(x) some continuous functions.Let g(x) = f1(x)*f2(x)*...*fn(x)What is the general form of the derivative of g ?   
d/dx g(x) = f2(x)*...fn(x)* d/dx f1(x) +  f1(x) * f3(x)...fn(x) * d/dx f2(x) +  f1(x) * f2(x) * f4(x)...fn(x) * d/dx f3(x) +  ...  f1(x)*...fn-1(x) * d/dx fn(x);  That's what I tought.  I just messed up when deriving I guess.  It didn't add up.  Thanks!  Edit: The rate-up didn't seem to be very effective tough. [grin]   