>>495

同じことだが、
 x-1 ≦ (x-1)x ≦ (x-1)x^2 ≦ (x-1)x^3 ≦ (x-1)x^4 ≦ (x-1)x^5,
 y-1 ≦ (y-1)y ≦ (y-1)y^2 ≦ (y-1)y^3 ≦ (y-1)y^4,
よって
 x^5 ≦ 1 + 5(x^6 -x^5),
 y^5 ≦ 1 + 5(y^5 -y^4),
辺々たす、だな。フムフム・・・