We just started partial derivatives in vector calculus and now we are being introduced to differentials.

I need to find the differential of (x^2 + y^3)^1/2 at the point (1,2)

I know that differential is equal to the sum of both partial derivatives so is the answer

3y^2 / (2(y^3 + x^2)^(1/2) + x/ (y^3 + x^2)^(1/2)