Originally Posted by

**alunw** The reason I say q2 is independent of r is because given

P(t) = (12*t)^(1/2)

S(r,t) = 10*r*t^2

y(r) = 20r.

q2(P,S,y) = 4*P*S^(-2)*y^2

then q2(t,r) = 4 * (12*t)^0.5 * 0.01 * r^-2 * t^-4 * 400 * r^2, and the terms in r cancel out completely so that in fact q2 only depends on t.

So when you calculate the partial derivative of q2 with respect to r the non-zero terms in r should cancel out.

In fact looking at your work you seem to have made a mistake calculating the partials of q2 with respect to both to P and S. Not sure why you've done that since you look OK on the q1 terms.