the sum of first 8 terms of an A.p is 100 and the sum of its first 19 term is 551 find the AP??
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S8=8/2 {2a+(8-1)d}
100=4 {2a+7d}
25=2a+7d. .................. (1)
S19=19/2 {2a+18d}
551=19/2 {2a +18d}
58={2a +18d }...........(2)
subtracting 2-1
11d=33
d=3
therfore for a
25=2a +7×3
25=2a +21
4=2a
a=2
so the Ap is 2 5 8 11...
100=4 {2a+7d}
25=2a+7d. .................. (1)
S19=19/2 {2a+18d}
551=19/2 {2a +18d}
58={2a +18d }...........(2)
subtracting 2-1
11d=33
d=3
therfore for a
25=2a +7×3
25=2a +21
4=2a
a=2
so the Ap is 2 5 8 11...
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