Antiderivative of: t rightarrow (1-t^{2})^{lambda)

Kendrick Finley

Kendrick Finley

Answered question

2022-10-18

Antiderivative of: t ( 1 t 2 ) λ
I would like to find an antiderivative of the function t ( 1 t 2 ) λ where λ R > 0 .
I really don't know how to proceed. One idea is to use the generalized binomial theorem to get:
( 1 t 2 ) λ = k = 0 ( λ k ) ( 1 ) k t 2 k
And by termwise integration I get that a possible antiderivative is k = 0 ( λ k ) ( 1 ) k t 2 k + 1 2 k + 1 .
The problem is that this form isn't really helpful. So is there a close form of this? So that I can study the behavior of the function when λ on [0,1], for example.

Answer & Explanation

imperiablogyy

imperiablogyy

Beginner2022-10-19Added 13 answers

Step 1
It turns out that no elementary function is the antiderivative you are looking for. The simplest answer makes use of the hypergeometric function:
f ( t ) = 2 F 1 ( 1 2 , λ , 3 2 , t 2 ) t + C
Step 2
The differential equation satisfied by 2 F 1 will then give f ( t ) = ( 1 t 2 ) λ .
You can then get a series around t = 0 to study the effect of λ. Intuitively, you'd expect (t) to go to infinity as λ for every non-zero t.
Kamden Larson

Kamden Larson

Beginner2022-10-20Added 1 answers

Explanation:
Let t = sin θ and substitute to get
( cos θ ) 2 λ + 1 d θ ..
This is still not a pretty anti-derivative (especially if λ is not an integer) but you know exactly what the graph looks like , so you can study the behavior as λ , perhaps.

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