An ap consists of 21 terms.The sum of three terms in the middle is 129 and of the last three is 237.Find the ap
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Answer:
3,7,11,15....
Step-by-step explanation:
The middle terms are 10,11,12th terms
therefore,
a+9d+a+10d+a+11d=129
3a+30d=129
a+10d=43 ------1
now,
adding last 3 terms
a+20d+a+19d+a+18d=237
3a+57d=237
a+19d=79 -------2
from 1 and 2
a=3
d=4
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