the sum of the first 9 terms of an Ap is 81 and that of its first 20 terms is 400 . find the first term and the common difference of an Ap.( mene method to sahi lagaya par mera answer correct nahi hai please help me!) (yaar koi to help kardo) ( jo bhi iska sahi answer dega mai usse follow karungi)
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Answer:
d=2,a=1
Step-by-step explanation:
S9=81
S20=400
9/2(2a+8d)=81
2(a+4d)=81*2/9=18
a+4d=9........1
10(2a+19d)=400
2a+19d=40.......2
from 1&2
2a-2a+19d-8d=40-18
11d=22
d=2
substitute in 1
a+8=9
a=1
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