x≠0 x^2>06/x^2+3x^2恒>0由均值不等式得6/x^2+3x^2≥2√(6×3)=6√2,当6/x^2=3x^2时,即当x^2=√2时取等号.不等式两边同时乘以-1,不等号方向改变：-6x^2-3x^2≤-6√2y=4-6/x^2-3x^2≤4-6√2当x^2=√2时,y有最大值yma...