- #1
Fernando Rios
- 96
- 10
- Homework Statement
- Find the interval of convergence of each of the following power series; be sure to investigate
the endpoints of the interval in each case.
- Relevant Equations
- ∑((√(x^2+1))^n 2^n/(3^n + n^3))
∑((√(x2+1))n22/(3n+n3))
We use the ratio test:
ρn = |2(3n+n3)√(x2+1)/(3n+1+(n+1)3)|
ρ = |2√(x2+1)|
ρ < 1
|2√(x2+1)| < 1
No "x" satisfies this expression, so I conclude the series doesn't converge for any "x". However the answer in the book says the series converges for |x| < √(5)/2. What am I dong wrong?
We use the ratio test:
ρn = |2(3n+n3)√(x2+1)/(3n+1+(n+1)3)|
ρ = |2√(x2+1)|
ρ < 1
|2√(x2+1)| < 1
No "x" satisfies this expression, so I conclude the series doesn't converge for any "x". However the answer in the book says the series converges for |x| < √(5)/2. What am I dong wrong?