Difference between revisions of "1971 Canadian MO Problems/Problem 6"
Airplanes1 (talk | contribs) (Created page with "== Problem == Show that, for all integers <math>n</math>, <math>n^2+2n+12</math> is not a multiple of <math>121</math>. == Solution == <math>n^2 + 2n + 12 = (n+1)^2 + 11</math...") |
(No difference)
|
Revision as of 22:42, 13 December 2011
Problem
Show that, for all integers , is not a multiple of .
Solution
. Consider this equation mod 11. .
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus not a multiple of 11, nor 121.
If , , thus a multiple of 11. However, considering the equation , , thus not a multiple of 121, even though it is a multiple of 11.
Thus, for any integer , is not a multiple of .
1971 Canadian MO (Problems) | ||
Preceded by Problem 5 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • | Followed by Problem 7 |