Question

若x=123456789×123456786，Y=123456788×123456787，试比较x,y大小，解：设123456788=a,

那么x=（a+1）(a-2)=a²-a-2，y=a(a-1)=a²-a∵x-y=（a²-a-2）-(a²-a)=-2＜0∴x＜y，请用这个方法算出1.345×0.345×2.69-1.345³-1.345×0.345²

Answer 1

0.345=a 1.345=a+1 2.69=2(a+1)
1.345×0.345×2.69-1.345³-1.345×0.345²
=(a+1)*a*2(a+1)-(a+1)^3-(a+1)*a^2
=2a(a+1)^2-(a+1)^3-a^2(a+1)
=(a+1)[2a(a+1)-(a+1)^2-a^2]
=-(a+1)
= -1.345