please , i'm french , so i didn't quite get the meaning of this sentence.
I also have not got it . Area on two dimensional manifold is a 2-form not 1-form
it's confusing and wasting my time .
thank you anyway.
The formula represents the area of a circular band on the sphere.
Like the shaded area in this image
In general is dA=R2sinθdθ but in that text they say that R=1.
Yes Nasu has got it right, the differential area of a sphere in spherical coordinates is:
##dA = R^2 sin \theta d\theta d\phi##
and integrating over ##d\phi##
and then setting R=1 you get
##Aring = 2\pi * sin \theta d\theta##
Thanks a lot guys.
that was very helpful
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