2x^2-axy+y^2<=0對任意x∈[1,2],y∈[1,3]恒成立,
<==>a>=2x/y+y/x①對任意x∈[1,2],y∈[1,3]恒成立,
設(shè)t=x/y,x∈[1,2],y∈[1,3],則t∈[1/3,2],
①變?yōu)閍>=2t+1/t,記為f(t),
t=1/√2時f(t)取最小值,
f(1/3)=11/3,f(2)=9/2,為最大值,
∴a>=9/2,為所求.