#1

The nth term of an arithmetic progression is 6+5n. Find the sum of the first 20 terms.

How do i find a and d? then i use the sum to 20 terms formula yea?

0
7 years ago
#2
substitute n=1,2,3 to find the first three terms and hence a and d.
0
7 years ago
#3
(Original post by razvimir)

The nth term of an arithmetic progression is 6+5n. Find the sum of the first 20 terms.

How do i find a and d? then i use the sum to 20 terms formula yea?

You know that the general nth term is a+(n-1)d. If you multiply out the brackets, you get a-d+dn=nth term. If you equate this to what you have above, you get 6+5n=a-d+dn. You can then work out a and d by equating the multiples of n and the constant term.
2
#4
omdz thats so simple! i was complicating it and overly thinking it. Thanks for your help
0
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