Question

find the sum of 25 terms of an AP in which the third term is 7 and seventh term is
2 more than its thrice third term​

Answer 1

Answer:

sum of 28 terms is 1175

Step-by-step explanation:

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Answer 2

Answer:

a3=7

a7=2+3(7)

a7=23

now,

a+2d=7-----------(1)

a+6d=23---------(2)

by allimination

d=4

substitute in any equation

a+2d=7

a+2(4)=7

a=7-8

=-1

by the some of natural numbers formulae

Sn=n/2(2a+(n-1)×d

S25=1175

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