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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.

2 answers

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
perfect