Find the no. of terms

Question

1. 3,5,7...33
2.-5,-1,3,...75

Solve each problem.
1. In the Arithmetic sequence 5,8,11,14.... what is n if a sub n is 32?
2.Find the sum of the first 20 terms of the arithmetic sequence -15,-7,31,43...

Answer 1

1. term(n) = a+(n-1)d
you have a = 3, d = 2 , n = ??
33 = 3 + (n-1)(2)
30 = 2n - 2
28 = 2n
n = 14 ------ there are 14 terms

do the 2nd one the same way

for the other two, I don't know how you defined a sub n

for the last:
first find the number of terms in the same way I showed you
you have a = -15 , d = 12 , n = ?
once you find a and d
use
Sum(n) = (n/2)(2a + (n-1)(d) )

Answer 2

Thank you so much . 1. In the Arithmetic sequence 5,8,11,14.... what is n if an is 32?
1. In the Arithmetic sequence 5,8,11,14.... what is n if n is 32?