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Find the sum of the infinite geometric series.\newline1+25+425+8125+1 + \frac{2}{5} + \frac{4}{25} + \frac{8}{125} + \dots\newlineWrite your answer as an integer or a fraction in simplest form.\newline__\_\_

Full solution

Q. Find the sum of the infinite geometric series.\newline1+25+425+8125+1 + \frac{2}{5} + \frac{4}{25} + \frac{8}{125} + \dots\newlineWrite your answer as an integer or a fraction in simplest form.\newline__\_\_
  1. Identify Terms and Ratio: First, we need to identify the first term aa and the common ratio rr of the geometric series.\newlineThe first term aa is 11.\newlineThe common ratio rr is the factor by which we multiply each term to get the next term. In this case, we multiply by 25\frac{2}{5} to get from one term to the next.\newlineSo, r=25r = \frac{2}{5}.
  2. Apply Geometric Series Formula: Next, we use the formula for the sum of an infinite geometric series, which is S=a1rS = \frac{a}{1 - r}, but only if the absolute value of rr is less than 11. Since r=25=0.4|r| = \left|\frac{2}{5}\right| = 0.4, which is less than 11, we can use the formula.
  3. Calculate Sum: Now, we plug the values of aa and rr into the formula to find the sum SS.\newlineS=1125S = \frac{1}{1 - \frac{2}{5}}
  4. Calculate Denominator: We calculate the denominator of the fraction: 125=5525=351 - \frac{2}{5} = \frac{5}{5} - \frac{2}{5} = \frac{3}{5}
  5. Find Final Sum: Now, we find the sum SS by dividing the first term by the result we just found: S=1(35)S = \frac{1}{(\frac{3}{5})}
  6. Multiply by Reciprocal: To divide by a fraction, we multiply by its reciprocal. So, we multiply 11 by 53\frac{5}{3}:S=1×(53)=53S = 1 \times \left(\frac{5}{3}\right) = \frac{5}{3}

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