Homework Help: Math

Posted by Aliza on Monday, January 21, 2013 at 5:16am.

Find the no. of terms
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...

Math - Reiny, Monday, January 21, 2013 at 10:34am
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) )
Math - Anonymous, Tuesday, January 22, 2013 at 6:52am
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?

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