P-SERIES OR HYPERHARMONIC TEST:
Theorem:- The infinite series
∑
1
𝑛 𝑝 =
1
1 𝑝+
1
2 𝑝+
1
3 𝑝+ …… is
convergent if p>1 and
divergent if p≤ 1.
Example:- test the series 𝑛=1
∞ 𝑛+1
(𝑛+2)2.
Let ∑un= 𝑛=1
∞ 𝑛+1
(𝑛+2)2 be a given series, where
un=
𝑛+1
(𝑛+2)2 is the nth term of the series. Choose an
auxiliary series ∑ vn, such that vn=
𝑛
𝑛2=
1
𝑛
.
Then, lim
𝑛→∞
𝑢 𝑛
𝑣 𝑛
=, lim
𝑛→∞
𝑛+1
(𝑛+2)2
1
𝑛
=, lim
𝑛→∞
𝑛+1
(𝑛+2)2 . 𝑛= lim
𝑛→∞
𝑛2 (1+
1
𝑛
)
𝑛2 (1+
2
𝑛
)2
= lim
𝑛→∞
(1+
1
𝑛
)
(1+
2
𝑛
)2
=
1+0
1+0
= 1≠0, a finite number.
Now, ∑vn=∑
1
𝑛
is divergent {∑
1
𝑛
𝑖𝑠 𝑝 − 𝑠𝑒𝑟𝑖𝑒𝑠 𝑤𝑖𝑡ℎ 𝑝 =
1 𝑖𝑛
1
𝑛 𝑝 }
Hence by comparison test, the given series
∑un= 𝑛=1
∞ 𝑛+1
(𝑛+2)2 is divergent.
THANK YOU

Test for convergence

  • 2.
    P-SERIES OR HYPERHARMONICTEST: Theorem:- The infinite series ∑ 1 𝑛 𝑝 = 1 1 𝑝+ 1 2 𝑝+ 1 3 𝑝+ …… is convergent if p>1 and divergent if p≤ 1.
  • 3.
    Example:- test theseries 𝑛=1 ∞ 𝑛+1 (𝑛+2)2. Let ∑un= 𝑛=1 ∞ 𝑛+1 (𝑛+2)2 be a given series, where un= 𝑛+1 (𝑛+2)2 is the nth term of the series. Choose an auxiliary series ∑ vn, such that vn= 𝑛 𝑛2= 1 𝑛 .
  • 4.
    Then, lim 𝑛→∞ 𝑢 𝑛 𝑣𝑛 =, lim 𝑛→∞ 𝑛+1 (𝑛+2)2 1 𝑛 =, lim 𝑛→∞ 𝑛+1 (𝑛+2)2 . 𝑛= lim 𝑛→∞ 𝑛2 (1+ 1 𝑛 ) 𝑛2 (1+ 2 𝑛 )2 = lim 𝑛→∞ (1+ 1 𝑛 ) (1+ 2 𝑛 )2 = 1+0 1+0 = 1≠0, a finite number. Now, ∑vn=∑ 1 𝑛 is divergent {∑ 1 𝑛 𝑖𝑠 𝑝 − 𝑠𝑒𝑟𝑖𝑒𝑠 𝑤𝑖𝑡ℎ 𝑝 = 1 𝑖𝑛 1 𝑛 𝑝 } Hence by comparison test, the given series ∑un= 𝑛=1 ∞ 𝑛+1 (𝑛+2)2 is divergent.
  • 5.

Editor's Notes