设x-y=α原式=16α²+40α+25 =(4α)²+2×20α+5² =(4α+5)²=0由平方数的非负性得 4α+5=0α=1.25则x-y=1.25
16(x-y)^2+40(x-y)+25=0设t=x-y∴16t²+40t+25=0(4t+5)²=0∴t=-5/4∴x-y=-5/4＜0∴x＜y
