Find the sum to n terms …

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Kth term=5k+1 1st term=5×1+1=6 2nd term=5×2+1=11 3rd term=5×3+1=16 A.P.6,11,16 a=6 d=11-6=5 n=n S=n/2{2a+(n-1)5} =n/2{2×6+(n-1)5 =n/2{12+5n-5} =n/2{7+5n}