令X = 2M,Y = 2N
M,N属于正整数.
有:
8M^2N + 8MN^2 = 8MN(M + N) = 96
MN(M + N) = 12
因M,N≥1,M + N≥2,根据基本不等式:
(M + N)^2/4 ≥ MN ≥ (M + N - 1)×1
快速判断下列方程:
M + N = 2,MN = 6无解
M + N = 3,MN = 4无解
M + N = 4,MN = 3,有解(M,N) = (1,3)
M + N = 6,MN = 2无解
M + N = 12,MN = 1无解
综上,(X,Y) = (2,6)
x的平方+y的平方 = 2^2 + 6^2 = 40