cho a,b > 0 và a+b = 1 . CM ab( $a^{2}$ + $b^{2}$ ) ≤ $\frac{1}{8}$

`a+b=1`

`⇒(a+b)^2=1`

`⇒a^2+2ab+b^2=1`

`⇒a=b=1/2`

`ab(a^2+b^2)`

`=1/2 . 1/2[(1/2)^2+(1/2)^2]`

`=1/4.(1/4+1/4)`

`=1/4. 1/2=1/8=1/8`

(`⇒` `text{đề sai}`)