Precalc

Find a formula for the nth term if...
a)the 8th term is 8 and the 20th term is 44
b) the 8th term is 4 and the 18th term is -96

thanks!! I am just confused how you do this if you don't know what n is.

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  1. I assume these are arithmetic sequences, so

    a)
    Tn = a+(n-1)d so
    a+7d = 8
    a+19d = 44
    12d = 36, so d=3
    a = -13

    or, you can do it like this.
    T20-T8 = 12d = 44-8 = 36, so d=3

    similarly, for
    b)
    10d = -100
    d = -10
    a = 74

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  2. perfect

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