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1+4+7+10+....+x=287 find x |
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Answer» a=1. d=3. Sn= 287. an=?Sn= n/2[2a+(n-1)d]287=n/2[2×1 +(n-1)3]287= n/2[2+3(n-1)]287= n/2[2+3n-3]287= n/2[3n-1]287×2 =n(3n-1)574= 3n^2 - n3n^2 - n - 574 =0Now,I hope you would solve. We need to find nHere,a=1 d=3 a n=287 n=?Therefore,An = a+(n-1)d287= 1+(n-1)3286=3n-3289=3n279/3=n93=n ANSWER |
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