$\mathrm { f } ( x )$ is a polynomial function defined for all real $x$.
Which of the following is a necessary condition for the inequality
$$\frac { \mathrm { f } ( a ) + \mathrm { f } ( b ) } { 2 } \geq \mathrm { f } \left( \frac { a + b } { 2 } \right)$$
to be true for all real numbers $a$ and $b$ with $a < b$ ?
..... 20
$\mathrm { f } ( x )$ is a polynomial function defined for all real $x$.

Which of the following is a necessary condition for the inequality

$$\frac { \mathrm { f } ( a ) + \mathrm { f } ( b ) } { 2 } \geq \mathrm { f } \left( \frac { a + b } { 2 } \right)$$

to be true for all real numbers $a$ and $b$ with $a < b$ ?