basically what i need is to find the area of the ring
the with is dr and the radius is r
so dA=pi*(r+dr)^2 - pi*(r)^2
so why the dA is that simple expression??
http://www.freeimagehosting.net/imag...cce537487f.gif
basically what i need is to find the area of the ring
the with is dr and the radius is r
so dA=pi*(r+dr)^2 - pi*(r)^2
so why the dA is that simple expression??
http://www.freeimagehosting.net/imag...cce537487f.gif