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Find a power series for 
f(x)=(4)/(8-x) centered at 2 and determine the interval of convergence. (6

Find a power series for f(x)=48x f(x)=\frac{4}{8-x} centered at 22 and determine the interval of convergence. (66

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Q. Find a power series for f(x)=48x f(x)=\frac{4}{8-x} centered at 22 and determine the interval of convergence. (66
  1. Rewrite Function: To find a power series for f(x)=48xf(x) = \frac{4}{8-x} centered at 22, we first rewrite the function in a form that allows us to use the geometric series formula. The geometric series formula is 11r=1+r+r2+r3+...\frac{1}{1-r} = 1 + r + r^2 + r^3 + ..., which converges when |r| < 1. We need to express f(x)f(x) in a similar form.
  2. Express as Geometric Series: We rewrite f(x)f(x) as f(x)=48x=46(x2)f(x) = \frac{4}{8-x} = \frac{4}{6-(x-2)}. This puts the function in a form where we can identify the 'r' term for the geometric series as (x2)6\frac{(x-2)}{6}.
  3. Expand into Power Series: Now we can express f(x)f(x) as a geometric series: f(x)=46(x2)=416(1x26)=2311x26f(x) = \frac{4}{6-(x-2)} = 4 \cdot \frac{1}{6 \cdot (1 - \frac{x-2}{6})} = \frac{2}{3} \cdot \frac{1}{1 - \frac{x-2}{6}}.
  4. Simplify Power Series: Using the geometric series formula, we expand f(x)f(x) into a power series: f(x)=23×(1+(x2)6+((x2)6)2+((x2)6)3+)f(x) = \frac{2}{3} \times \left(1 + \frac{(x-2)}{6} + \left(\frac{(x-2)}{6}\right)^2 + \left(\frac{(x-2)}{6}\right)^3 + \ldots\right).
  5. Final Power Series: To simplify the power series, we distribute the 23\frac{2}{3} across the series: f(x)=23+(x2)9+(x2)254+(x2)3324+f(x) = \frac{2}{3} + \frac{(x-2)}{9} + \frac{(x-2)^2}{54} + \frac{(x-2)^3}{324} + \ldots
  6. Interval of Convergence: The power series for f(x)f(x) is now expressed as: f(x)=n=0(x2)n3n+1f(x) = \sum_{n=0}^{\infty} \frac{(x-2)^n}{3^{n+1}}.
  7. Check Endpoints: Next, we need to determine the interval of convergence for the power series. The series converges when |\frac{x-2}{6}| < 1, which means -1 < \frac{x-2}{6} < 1.
  8. Check Endpoints: Next, we need to determine the interval of convergence for the power series. The series converges when |\frac{x-2}{6}| < 1, which means -1 < \frac{x-2}{6} < 1.Solving the inequality for xx gives us -6 < x-2 < 6, which simplifies to -4 < x < 8.
  9. Check Endpoints: Next, we need to determine the interval of convergence for the power series. The series converges when |\frac{x-2}{6}| < 1, which means -1 < \frac{x-2}{6} < 1.Solving the inequality for xx gives us -6 < x-2 < 6, which simplifies to -4 < x < 8.We must check the endpoints x=4x = -4 and x=8x = 8 to see if the series converges at these points. For x=4x = -4, the series becomes 48(4)=412=13\frac{4}{8-(-4)} = \frac{4}{12} = \frac{1}{3}, which is a finite number. For x=8x = 8, the series is undefined because it would involve division by zero. Therefore, the interval of convergence is -1 < \frac{x-2}{6} < 100.

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