Let f:[0,2] → R be a twice differentiable function such that f^′ ′(x)>0, for all x ∈(0,2). If φ(x)=f(x)+f(2-x), then φ is:

Let $\displaystyle f:[0,2] \rightarrow \mathbf{R}$ be a twice differentiable function such that $\displaystyle f^{\prime \prime}(x)>0$, for all $\displaystyle x \in(0,2)$. If $\displaystyle \phi(x)=f(x)+f(2-x)$, then $\displaystyle \phi$ is :