04 May '05 06:59>
Find all pairs of positive integers x and y that safisfy the equation:
1/x - 1/y = 1/2005
1/x - 1/y = 1/2005
Originally posted by PBE6Anayltically? I don't think there's a magic method of doing this, but it's easy to show rigorously that you've found all the solutions: all you need to do is remark that for all solutions in positive integers,
OK, here's what I got:
x = 1600; y = 8020
x = 1980; y = 158796
x = 2000; y = 802000
x = 2004; y = 0 is another pair, but 0 is not a positive integer.
Sadly, I solved this by trial and error. :'( If anyone knows how to do this analytically, I'd love to find out how.
Originally posted by AcolyteOops, my mistake (with the 0).
Anayltically? I don't think there's a magic method of doing this, but it's easy to show rigorously that you've found all the solutions: all you need to do is remark that for all solutions in positive integers,
1/x < 1/2005, so x < 2005,
and find y for each x in turn, confirming that the solutions you listed below are the only ones in positive integers.
1/2004 -1/0 is -infinity though, so that's not a solution at all.
Originally posted by PBE6I think your 1600 should be 1604.
OK, here's what I got:
x = 1600; y = 8020
x = 1980; y = 158796
x = 2000; y = 802000
x = 2004; y = 0 is another pair, but 0 is not a positive integer.
Sadly, I solved this by trial and error. :'( If anyone knows how to do this analytically, I'd love to find out how.
Originally posted by davegageOops again. I think my blood sugar is low. I need a cookie.
I think your 1600 should be 1604.
x must be < 2005; so we need to find those values of x such that y = 2005x/(2005 - x) is also an integer.
Here's what I get for (x,y), and I think this is all such pairs:
(1604, 8020)
(1980, 158796)
(2000, 802000)
(2004, 4018020)
EDIT: I don't see any magical analytical solution either, although the problem can be whittled down quite a bit.
Originally posted by PBE6Let a,b be relatively prime integers , and x=ka and y=kb, b>a
Oops again. I think my blood sugar is low. I need a cookie.
Acolyte, bring me your head again.