Precalc
posted by Rebekah on .
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.

I assume these are arithmetic sequences, so
a)
Tn = a+(n1)d so
a+7d = 8
a+19d = 44
12d = 36, so d=3
a = 13
or, you can do it like this.
T20T8 = 12d = 448 = 36, so d=3
similarly, for
b)
10d = 100
d = 10
a = 74