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How many terms of the arithmetic sequence 5, 7,9to get 140?must be added |
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Answer» a=5d=7-5=2 S=(n/2)*(2a+(n-1)*d)140=(n/2)*(2*5+(n-1)*2)140=(n/2)*(10+2n-2)280=8n+2n²2n²+8n-280=0n²+4n-140=0n²+14n-10n-140=0n(n+14)-10(n+14)=0(n-10)(n+14)=0n=10,-14 -14 is not possible Hence number of terms requires to produce a sum of 140= 10 |
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