Given: sum of first three terms is 27

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 = 27

3a = 27

a = 9

given that the product of three terms is 648

so a³ - ad² = 648

substituting a = 9

9³ - 9d² = 648

729 - 9d² = 648

81 = 9d²

d = 3 or d = - 3

hence the given terms are a - d, a, a + d which is 6, 9, 12 or 12, 9, 6