Question

5 times of 5th term is equal to 8 times of 8th term of an arithmetic sequence then find the sum of first 25 term
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Answer 1

Answer:

given , 5(a + 4d) = 8(a + 7d)

=> 5a + 20d = 8a + 56d

=> -3a - 36d = 0

=> a + 12d = 0 [ divide both sides with -3]

S25 = 25/2 [ 2a + 24d ]

=> 25/2*2 [ a + 12d] [ factor out 2 ]

=> 25 × 0

=> 0 answer