solving quadratic equation
2012-09-30 2:15 am
it si given that 1+2+3..+n=1/2(n+1),wher n is a positive integer. if 11+12+13+....+n=410,find the value of n.
回答 (1)
2012-09-30 2:32 am
✔ 最佳答案
11 + 12 + 13 + .. + n = 410n(n + 1)/2 - 55 = 410
n(n + 1)/2 = 465
n(n + 1) = 930
n = 30
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