9t-2n=-11 .......(1)
{
2n(n-1)-18nt+36t=46 .......(2)
From(1), n=(9t+11)/2 .......(3)
Sub(3)into(2),
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請大家教教我~
with詳細的步驟please!!!
[MATHS]Solve equations 1題
2009-10-17 2:35 am
回答 (1)
2009-10-17 2:56 am
✔ 最佳答案
Sub into (2) we get2[(9t + 11)/2][(9t + 11)/2 - 1] - 18t[(9t + 11)/2] + 36t = 46
(9t + 11)[(9t + 11 - 2)/2] - 9t(9t + 11) + 36t = 46
(9t + 11)(9t + 9) - 18t(9t + 11) + 72t = 92
81t^2 + 180t + 99 - 162t^2 - 198t + 72t - 92 = 0
- 81t^2 + 54t + 7 = 0
(-9t - 1)(9t - 7) = 0
so -9t = -1, t = 1/9 and
9t - 7 = 0, t = 7/9.
When t = 1/9, n = 6
when t = 7/9, n = 9.
2009-10-16 19:01:03 補充：
Correction : Line 8 should be -9t = 1. so t = -1/9, n = 5.
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