vault backup: 2025-10-13 16:10:57
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@@ -143,3 +143,8 @@ The behavior a given power series falls into one of three cases:
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1. Solving for any power series usually starts with the ratio test.
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1. Solving for any power series usually starts with the ratio test.
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1. Create a ratio with $n + 1$ and $n$.
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1. Create a ratio with $n + 1$ and $n$.
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$$ \frac{x^{n+1}}{3^{n+1}} \cdot \frac{3^n}{x^n} $$
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$$ \frac{x^{n+1}}{3^{n+1}} \cdot \frac{3^n}{x^n} $$
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2. Cancel stuff out
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$$ \frac{x}{3}$$
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2. For a geometric series, it converges when the ratio $r$ is less than one. Written as an equality, this gives us:
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$$ |r| < 1 \to |\frac{x}{3}| < 1 \to |x| < 3 $$
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This means that the interval of convergence is $(-3, 3)$
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