Ratio and root convergence tests
If |aₙ₊₁/aₙ|→ρ, or |aₙ|¹⁄ⁿ→ρ, then Σaₙ converges absolutely for ρ<1 and diverges for ρ>1.
Key knowledge
If |aₙ₊₁/aₙ|→ρ, or |aₙ|¹⁄ⁿ→ρ, then Σaₙ converges absolutely for ρ<1 and diverges for ρ>1. At ρ=1 either behavior is possible.
Conditions and scope
- The ratio test requires eventually nonzero aₙ; the root test does not.
- These stated limit forms are inconclusive if the indicated limit fails to exist.
Sources · 1
References
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Evidence and review
Theorems 5.16–5.17; the strict inequality and inconclusive equality cases are retained.
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Entry details
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- university-core.1
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- University core expansion