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8 April, 16:12

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?

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  1. 8 April, 18:07
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    first term a=4

    Step-by-step explanation:

    Sum of the first 6 terms S6 = 15624

    common ratio r = 5

    n = 6

    first term a=?

    Formula: S6 = a (r^n-1) / r-1

    15624 = a (5^6-1) / 5-1

    15624 = a (15625-1) / 4

    15624 = a (15624) : 4

    15624 = 15624a:4

    Cross multiply

    15624*4 = 15624a

    62496 = 15624a

    divide both sides by 15624

    62496:15624 = 15624a:15624

    4 = a

    a = 4
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