Question

In an ap if the 6th and 13th term are 35 and 70 respectively find the sum of its first 20 terms

Answer 1

Answer:

Step-by-step explanation:

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Answer 2

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HERE IS THE ANSWER TO YOUR QUESTION........

let a be first term and d the common differece of an A.P:-

According to given condition:-

a6=35.

a13=70.

a+5d=35 -----(1)

a+12d=70------(2)

Substracting (1) from (2),we get,

7d=35

d=5

Substituting d=5 in (1)

a+25=35

a=10

then sum of its first 20 terms is

=20/2[2a+(20-1)d]

=10[2*10+19*5]

=10*115

=1150.

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