For what values of p and q will $\sum\limits_{n=2}^{\infty }{ \frac{1}{n^p\times(\ln(n))^q} }$ converge?
For what values of p and q will ∞∑n=21np×(ln(n))q converge?
For sufficiently large n independent of p and q, n>ln(n), so np is dominant.
p>1,
∞∑n=21np×(ln(n))q≤∞∑n=21np
∞∑n=21np converges, so ∞∑n=21np×(ln(n))q converges for all q.p=1,
∞∑n=21n diverges(it’s harmonic numbers).
But using integral test, ∫∞21x×(lnx)qdx=[1(−q+1)×(lnx)q−1]∞2, range of q can be divided.- q>1
∞∑n=21np×(ln(n))q=∞∑n=21n×(ln(n))q converges. - q<1
∞∑n=21np×(ln(n))q=∞∑n=21n×(ln(n))q diverges. - q=1
∫∞21x×(lnx)qdx=[lnx]∞2 diverges.
- q>1
p<1,
∞∑n=21np×(ln(n))q≥∞∑n=21np
∞∑n=21np diverges, so ∞∑n=21np×(ln(n))q diverges for all q.
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