# I Subscript derivative notation

1. Apr 25, 2016

### Abdul.119

I have an equation that looks like

At, r = Aφ, r

If I know that Aφ = r4 , then how do I find At ?

I believe that the above equation is equivalent to: ∂/∂r (At) = ∂/∂r (Aφ) , correct?

Then substitute the value Aφ and we have ∂/∂r (At) = ∂/∂r (r4)

And then to get At I take the integral on both sides? so eventually At = r5/5 ?

2. Apr 25, 2016

### Staff: Mentor

Yes, $A_{t, r}$ is notation that means $\frac{\partial}{\partial r}\frac{\partial A}{\partial t}$
Yes. Integrate with respect to r.
Are r and t independent of each other. If so, the above looks fine.