Cho số thực dương a,b,c thỏa mãn a+b+c=3. Chứng minh rằng
a3+8≥2(ab+bc+ca)27+19.the fraction with numerator a squared and denominator b cubed plus 8 end fraction plus the fraction with numerator b squared and denominator c cubed plus 8 end fraction plus the fraction with numerator c squared and denominator a cubed plus 8 end fraction is greater than or equal to the fraction with numerator 2 open paren a b plus b c plus c a close paren and denominator 27 end fraction plus one-nineth point