kieuthuyduong

A=a+1/b²+1 + b+1/c²+1 + c+1/a²+1

a+b+c-A= (a- a+1/b        ² +1) + (b- b+1/c²+1) + (c- c+1/a²+1) 

3-A= ab²-1/b²+1 + bc²-1/c²+1 + ca²-1/a²+1

3-A <= ab²-1/2b + bc²-1/2c + ca²-1/2a

3-A <= 0,5(ab+bc+ca) - 0,5(1/a+1/b+1/c)

3-A <= 3/- 9/2(ab+bc+ca)

3-A <= 3/-3/2

3-A <= 0

A => 3

dấu bằng xảy ra <=> a=b=c=1

Giai thich cho mik đoạn 

3-A <= 3/- 9/2(ab+bc+ca)

3-A <= 3/-3/2

3-A <= 0

A => 3

với nhé mk ko hiểu lắm