Answer:
-41
Step-by-step explanation:
arithmetic sequence formula:
[tex]an = a1 + (n - 1)d[/tex]
where an = nth term , a1 = first term, n = # of terms and d = common difference
we want to find the 21st terms
The first term is -1 so a1 = -1
The number of terms is 21 so n = 21
and the common difference appears to be -2 because as the sequence goes on the number previous to it is subtracted by 2. eg. to get to -3 from -1 we subtract 2 ( -1 - 2 = -3) so d = -2
to find the 21st term we plug in the values of the variables
an = a1 + (n-1)d
a1 = -1 , n = 21 and d = -2
an = -1 + (21-1)(-2)
subtract 1 from 21
an = -1 + (20)(-2)
multiply -2 and 20
an = -1 + -40
add -1 and -40
an = -41
the 21st term would be -41
