i was looking through a book and came across a double integral that was split into the product of two single integrals. it was int (x^n)(y^n ) dxdy split into (int x^n dx)(int y^n dy) i just finished a course in multivariable calculus(it was by no means thorough), and i didn't know that you could do this. is this a general rule? a typo? a special case? thanks in advance.