# Question #e4948

##### 2 Answers

#### Explanation:

For the standard

#color(blue)"arithmetic sequence"#

#a,a+d,a+2d,a+3d,......,a+(n-1)d# where a

#=a_1# is the first term, d the common difference and n the number of terms.and

#d=a_2-a_1=a_3-a_2= ....=a_n-a_(n-1)#

#color(blue)"The sum to n terms" = color(red)(bar(ul(|color(white)(2/2)color(black)(S_n=n/2[2a+(n-1)d])color(white)(2/2)|)))# A series is the sum of the terms in the sequence.

Here

#a=1, d=6-1=11-6=5" and " n=20#

#rArrS_20=20/2[(2xx1)+(19xx5)]#

#=10(2+95)=970#

#### Explanation:

We have:

This is an arithmetic sequence with a common difference of

First, let's determine the number of terms in the sequence:

Then, let's evaluate the sum of the