SOLUTION: find the sum of the first 20 terms in the series 1,5,9,13,17...

Click here to see ALL problems on Trigonometry-basics

Question 936142: find the sum of the first 20 terms in the series 1,5,9,13,17...
Found 3 solutions by josgarithmetic, srinivas.g, MathTherapy:
Answer by josgarithmetic(39625)   (Show Source):
You can put this solution on YOUR website!
common difference is +4.

is the sum you want. Do you know how to find the "LastTerm" ?

Answer by srinivas.g(540)   (Show Source):
You can put this solution on YOUR website!
Given series is 1,5,9,13,17....
first term (a)= 1
difference b/w first term and second term = 5-1 =4
difference b/w second and third term = 9-5=4
every where difference b/w two consecutive terms is 4
hence the give series is Arithmetic series
formula ;
where n= no of terms
d is common difference
n= 20
d= 4
a = 1
sum =
=
=
=
=780
Result : sum =780

Answer by MathTherapy(10555)   (Show Source):
You can put this solution on YOUR website!

find the sum of the first 20 terms in the series 1,5,9,13,17...

To determine the sum, use the formula for the sum of an AP, with number of terms, 1st term, and common difference (d), known.
Formula:
------ Substituting 20 for n, 1 for , and 4 for common difference , or d

Sum of 1st 20 terms, or