x=1.345×0.345×2.69y=1.345³-1.345×0.345²
设a=0.345
x=(a+1)×a×2(1+a)
=2a(a+1)²
y=(1+a)³-(1+a)×a²
=(a+1)[(a+1)²-a²]
=(a+1)(2a+1)
x-y=2a(a+1)²-(a+1)(2a+1)
=(a+1)[2a(a+1)-(2a+1)]
=(a+1)(2a²-1)
∵(a+1)＞0(2a²-1)＜0
∴(a+1)(2a²-1)＜0
x-y＜0
x＜y
∴1.345×0.345×2.69-1.345³-1.345×0.345²＜0是计算x-y=2a(a+1)²-(a+1)(2a+1) =(a+1)[2a(a+1)-(2a+1)] =(a+1)(2a²-1)带入a=0.345就是了