- #1
Unit
- 182
- 0
I read this in the appendix of Hardy's pure mathematics textbook and an explanation was not given:
[tex]\lim_{x \to 1} \sum_1^\infty \left( x^{n-1}-x^n \right) = \lim_{x \to 1} \left( 1 - x + (x - x^2) + \ldots \right) = \lim_{x \to 1} 1 = 1[/tex]
[tex]\sum_1^\infty \lim_{x \to 1} \left( x^{n-1}-x^n \right) = \sum_1^\infty \left( 1 - 1 \right) = 0 + 0 + 0 + \ldots = 0[/tex]
Are both answers correct? I thought that associativity only applied to a finite series of operations, which is why I think the first equation is wrong.
[tex]\lim_{x \to 1} \sum_1^\infty \left( x^{n-1}-x^n \right) = \lim_{x \to 1} \left( 1 - x + (x - x^2) + \ldots \right) = \lim_{x \to 1} 1 = 1[/tex]
[tex]\sum_1^\infty \lim_{x \to 1} \left( x^{n-1}-x^n \right) = \sum_1^\infty \left( 1 - 1 \right) = 0 + 0 + 0 + \ldots = 0[/tex]
Are both answers correct? I thought that associativity only applied to a finite series of operations, which is why I think the first equation is wrong.