以下均采用基本不等式(x+y)^2/2+(x+y)/4>=[(x+y)*2√xy]/2+(2√xy)/4=(√xy)(x+y+1/2)=(√xy)[(x+1/4)+(y+1/4)]>=(√xy)(√x+√y)=x√y+y√xa^2*(5+a^3)-(1+5a^3)=(a-1)^3(a^2+3a+1)a^2