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How many terms of the A.P. 3,5,7... Must be taken so that the sum is 120? |
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Answer» a=3d=2n=?sn=n/2(2a+(n-1)d)=120n/2(6+2n - 2)=1203n+n2-n=120n2+2n-120=0n2+12n-10n-120=0n(n+12) - 10(n+12)=0n = 10n= -12 not possiblecheck ur answer s10 = 10/2(2a+18) = 5(6+18) = 5x24=120 a=3,d=2,n=?,An=120So if we use the formulaAn=a+(n-1)d120=3+(n-1)2120=3+2n-2120=1+2n120÷2=n+160=n+160-1=nn=59 |
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