Using root test and ratio test for divergence

superdave
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Homework Statement



Does this series converge or diverge?

Series from n=1 to infinity n(-3)^(n+1) / 4^(n-1)



Homework Equations





The Attempt at a Solution



Okay, I've tried it both ways.

Ratio test:

lim n --> inf. ((n+1)*(-3)^(n+1)/4^n) / (n * (-3)^n / 4^(n-1))

Now, that doesn't appear to simplify in anyway that would make using l'hospital's rule possible to find the limit.

Root test:

lim n --> inf. of -3*n^(1/n) / 4^((n-1)/n)

That bottom part throws me off.
 
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Why does it through you off? What is the limit of (n-1)/n as n goes to infinity?
 
superdave said:

Homework Statement



Does this series converge or diverge?

Series from n=1 to infinity n(-3)^(n+1) / 4^(n-1)



Homework Equations





The Attempt at a Solution



Okay, I've tried it both ways.

Ratio test:

lim n --> inf. ((n+1)*(-3)^(n+1)/4^n) / (n * (-3)^n / 4^(n-1))

Now, that doesn't appear to simplify in anyway that would make using l'hospital's rule possible to find the limit.
Seriously? You are aware, are you not, that (-3)^(n+1)/(-3)^n= -3? The (4^n part is just as easy! You should not need L'Hospital's rule.

Root test:

lim n --> inf. of -3*n^(1/n) / 4^((n-1)/n)

That bottom part throws me off.
 
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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