Question

find the sum of 20 terms 1,4,7,20 and so on

pls and this question


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Answer 1

Answer:

(2a+(n−1)d)

wheres

n

=sumofnterms

a=firstterm

d=difference

n=numberofterms

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=> 1st term (a) = 1

=> difference (d ) = (4-1)=(7-4)=3

=> Sum of 20 terms

2

20

((2×1)+(20−1)3)

=10(2+(19×3))

=10(2+57)=59×10

=

590

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