Finding the Interval for Power Series Summation of x^(n)/[2^(n)*n^(4)]

frasifrasi
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For summation from 1 to infinity of x^(n)/[2^(n)*n^(4)]
- I get the radius is 2 by ration test, but how do I get the interval, just by pluggin in?
 
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anyone? : )
 
well it's just -1<x<1

so your R is 2, but before you had x/2

-1<x/2<1

-2<x<2 (equal to)
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...

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