1.

2) Determine the sum of first 35 terms of an AP if its secondterm is 2 and seventh term is 22.

Answer»

we have given that the second term of AP = 2 and seventh term =22we have to findthe sum of first 30 terms of an A.P.=?solution:-using formula:An = a+(n-1) d

here ;given thata2 = 2 => a+d = 2 ....................(1)&a7= 22 => a+6d = 22....................(2)

solving (1)&(2) we get(2-d) +6d = 22=> 5d = 22-2= 20=> d= 4now put the value of d in (1) we geta+4= 2=> a= -2

now ,using formula:Sn = n/2{2a +(n-1) d}

the sum of first 30 terms of an A.P.=here n= 30

=30/2 {2×(-2) +(30-1)×4}= 15 {-4 +120 - 4}= 15 × 112= 1680

hence ;the sum of first 30 terms of an A.P.=1680 answer


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