Q. The sum of the first 6 terms of a geometric series is 15624 and the common ratio is 5. What is the first term of the series?
Define Terms: Let's denote the first term of the geometric series as a, and the common ratio as r. The sum of the first n terms of a geometric series is given by the formula Sn=(1−r)a(1−rn), where Sn is the sum of the first n terms, a is the first term, and r is the common ratio. We are given that S6=15624 and r=5.
Substitute Values: Substitute the given values into the sum formula for a geometric series to find the first term a.S6=(1−r)a(1−r6)15624=(1−5)a(1−56)
Calculate Exponents: Calculate the value of 56 and substitute it into the equation.56=1562515624=a(1−15625)/(1−5)
Simplify Equation: Simplify the equation by performing the operations inside the parentheses.15624=a(1−15625)/(−4)15624=a(−15624)/(−4)
Divide and Solve: Simplify the equation further by dividing −15624 by −4.15624=a(−4−15624)15624=a(3916)
Divide and Solve: Simplify the equation further by dividing −15624 by −4.15624=a(−15624)/(−4)15624=a(3916)Solve for a by dividing both sides of the equation by 3916.a=15624/3916a=4
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