20/11/02 17:54:01.51 nV+GRV6y.net
XX-YY = (X+Y)(X-Y),
X+Y と X-Y は共に偶数 or 共に奇数。
本問では両方とも偶数。
(X+Y)/2 = s, (X-Y)/2 = t (s>t>0)とおくと
st = (X+Y)(X-Y)/4 = (XX-YY)/4 = 15,
(s,t) = (15,1) or (5,3)
(X,Y) = (s+t, s-t) = (16,14) or (8,2)
20/11/02 17:54:01.51 nV+GRV6y.net
XX-YY = (X+Y)(X-Y),
X+Y と X-Y は共に偶数 or 共に奇数。
本問では両方とも偶数。
(X+Y)/2 = s, (X-Y)/2 = t (s>t>0)とおくと
st = (X+Y)(X-Y)/4 = (XX-YY)/4 = 15,
(s,t) = (15,1) or (5,3)
(X,Y) = (s+t, s-t) = (16,14) or (8,2)