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The sum of the first 6 terms of a geometric series is 15,624 and the common ratio is 5 .
What is the first term of the series?

The sum of the first 66 terms of a geometric series is 1515,624624 and the common ratio is 55 .\newlineWhat is the first term of the series?

Full solution

Q. The sum of the first 66 terms of a geometric series is 1515,624624 and the common ratio is 55 .\newlineWhat is the first term of the series?
  1. Formula Application: The sum of the first nn terms of a geometric series can be found using the formula Sn=a(1rn)(1r)S_n = \frac{a(1 - r^n)}{(1 - r)}, where SnS_n is the sum of the first nn terms, aa is the first term, rr is the common ratio, and nn is the number of terms. We are given that S6=15,624S_6 = 15,624, r=5r = 5, and n=6n = 6. We need to solve for aa.
  2. Plug Known Values: First, let's plug the known values into the formula for the sum of a geometric series:\newlineS6=a(156)/(15)S_6 = a(1 - 5^6) / (1 - 5)\newline15,624=a(115625)/(15)15,624 = a(1 - 15625) / (1 - 5)
  3. Simplify Equation: Now, let's simplify the denominator and the numerator inside the parentheses:\newline15,624=a(115625)/(4)15,624 = a(1 - 15625) / (-4)\newline15,624=a(15624)/(4)15,624 = a(-15624) / (-4)
  4. Divide by Constant: Next, we simplify the right side of the equation by dividing 15624-15624 by 4-4:15,624=a(3906)15,624 = a(3906)
  5. Final Division: To find the value of aa, we divide both sides of the equation by 39063906:a=15,6243906a = \frac{15,624}{3906}
  6. Find Value of a: Now, we perform the division to find the value of aa:a=4a = 4

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