If 6th terms of an A.P.is 121 then find the sum of its firest 11 terms.
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6th term of an ap will be given by a+5d .
do a+5d=121
now, sum of first 11 terms . here n=11,
s11=n÷2[2a+(n-1)d]
s11=11÷2[2a+(11-1)d]
s11=11/2[2a+10d]
s11=11/2×2[a+5d]
s11=11×[a+5d]
s11=11×121
s11=1331
do a+5d=121
now, sum of first 11 terms . here n=11,
s11=n÷2[2a+(n-1)d]
s11=11÷2[2a+(11-1)d]
s11=11/2[2a+10d]
s11=11/2×2[a+5d]
s11=11×[a+5d]
s11=11×121
s11=1331
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