maths(17) - 複習題

2011-06-19 10:35 pm
設f(x) = (x - 1)(x - 2)....(x - 9)(x - 10),
試求f[(f(x)]除以f(x)之餘式。


試求最大的正整數x,
使得x^2 - 10x + 112為一完全平方數。

回答 (1)

2011-06-20 12:42 am
✔ 最佳答案
1)f[f(x)] = (f(x) - 1) (f(x) - 2) (f(x) - 3) ... (f(x) - 10)= K f(x) + 10!f[(f(x)]除以f(x)之餘式 = 10!
2)令x² - 10x + 112 = k²(x² - 10x + 25) + 87 = k²k² - (x - 5)² = 87(k - x + 5)(k + x - 5) = 87 = 3*29Case 1 :k - x + 5 = 3
{
k + x - 5 = 29解之得 : k = 16 , x = 18
Case 2 :k - x + 5 = 29
{
k + x - 5 = 3解之得 : k = 16 , x = - 8
Case 3 :k - x + 5 = - 3
{
k + x - 5 = - 29解之得 : k = - 16 , x = - 8
Case 4 :k - x + 5 = - 29
{
k + x - 5 = - 3解之得 : k = - 16 , x = 18
Case 5 :k - x + 5 = 1
{
k + x - 5 = 87解之得 : k = 44 , x = 48
Case 6 :k - x + 5 = 87
{
k + x - 5 = 1解之得 : k = 44 , x = - 38
Case 7 :k - x + 5 = - 1
{
k + x - 5 = - 87解之得 : k = -44 , x = -38
Case 8 :k - x + 5 = - 87
{
k + x - 5 = - 1解之得 : k = -44 , x = 48最大的正整數 x = 48


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