f(x):[0,2]→R and f′′(x)>0 for x∈[0,2]
⇒f′(x) is increasing for x∈[0,2]
Now, ϕ(x)=f(x)+f(2−x)
⇒ϕ′(x)=f′(x)−f′(2−x)
For x∈[0,1) , x<2–x
⇒f′(x)<f′(2−x)⇒ϕ′(x)<0
For x∈(1,2] , x>2–x
⇒f′(x)>f′(2−x)⇒ϕ′(x)>0
Hence, ϕ is decreasing on (0,1) and increasing on (1,2).