Answer:
an = 3n - 3
Explanation:
The nth term of an arithmetic progression is expressed as;
an = a + (n-1)d
a is the first term
n is the number of terms
d is the common difference
a8 = a + (8-1)d
a8 = a + 7d = 21 ....1
a10 = a+9d = 27 ....2
Subtract 1 from 2
7d - 9d = 21 - 27
-2d = -6
d = -6/-2
d = 3
Since a + 7d = 21
a + 7(3) = 31
a + 21 = 21
a = 21 - 21
a = 0
Get the nth term
Recall that an = a + (n-1)d
an = 0 + (n-1)*3
an = 3n - 3
Hence the nth term of the sequence is 3n - 3