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The sum of the first n terms of an AP whosefirst term is 8 and the common difference is20, is equal to the sum of first 2n terms oanother AP whose first term is -30 and thecommon difference is 8. Find the value of nNCERT Exempla |
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Answer» Sum of first n terms Sn=n/2[2a+(n-1)*d]n/2[2×8+(n-1)×20]=2n/2[2×-30+(2n-1)×8]16+20n-20=2(-60+16n-8)-4+20n=2(-68+16n)-2+10n=-68+16n66=6nn=11 |
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