Q. 74.3( 6 Votes )

# The Sum of

Answer :

Given: the sum of first three terms is 21

To find: the first three terms of AP

Assume the first three terms are a - d, a, a + d where a is the first term and d is the common difference

So, sum of first three terms is a - d + a + a + d = 21

3a = 21

a = 7

it is also given that product of first and third term exceeds the second by 6

so (a - d)(a + d) - a = 6

a2 - d2 - a = 6

substituting a = 7

72 - d2 - 7 = 6

d2 = 36

d = 6 or d = - 6

Hence the terms of AP are a - d, a, a + d which is 1, 7, 13 or 13, 7, 1

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