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ii) given an-4, d-2. Sll_-14, find n and a. |
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Answer» an=a+(n-1)d=4a+(n-1)2=4 a+2n-2=4a+2n=4+2a+2n=6a=6-2nsn=n/2[2a+(n-1)d]=-14 n/2[2a+(n-1)2]=-14 an+n(n-1)=-14(6-2n)n+n²-n=-146n-2n²+n²-n=-14-n²+5n=-14n²-5n=14n²-5n-14=0 n²-7n+2n-14=0 n(n-7)+2(n-7)=0(n-7)(n+2)=0either, n-7=0or, n=7or, n+2=0or, n=-2∵, n can not be negative ;∴, n=7∴, a=6-(2×7)=6-14=-8∴, n=7 and a=-8 |
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