Integrals

So explain me this, I have never studied integrals and suddenly im faced with them while calculating work of electric fields.

why does a S(0,1 to infinity ) of 1/(4.Pi.E0.((15.10^6)/r^2).er.dr

equals (15.10^6)/(4.Pi.E0 ?
specifically, how do integrals work?

http://www.mathematicshelpcentral.com/lecture_notes/calculus_2_folder/introduction_to_integral_calculus.htm

Also, write your integral more clearly. I can't make heads or tails of it.

S ( 0,1 to infinity ) dr/r^2
removed the constants.

Integration is effectively the opposite of differentiation.
So Sar^n dr = a/(n+1)r^n+1 (plus constant) because, if you differentiate that, you get ar^n. The constant is known as the constant of integration; it's arbitrary because it disappears if you differentiate it.

In your case, a is the constant you removed, and n=-2.

Why are you calculating work if you haven't taken calculus?

Math first, physics second.

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You can also think of definite integrals as area under a curve

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