The third term of an ap is 8 and ninth term of it exceeds three times the third term by 2 find the sum of first 19 terms
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It is given that ,
a+2d=8. ......(1)
a+8d=3×8+2=26. ......(2)
a=8-2d (from (1))
Put the value of( a )in (2)
a+8d=26
8-2d+8d=26
8+6d=26
6d=26-8
6d=16
d=16/6now put the value of d in any eq.. and then value of (a) will be 6
s19=19/2×2a+18d
Then s19=570
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