vì f(x)+2f(2-x)=x+1 => PT f(x) có dạng ax+b.
ta có f(x)+2.f(2-x)=ax+b+2(a(x-2)+b)
=ax+b-2ax+4a+2b=-ax+4a+3b=x+2
ta có hệ :
\(\left\{{}\begin{matrix}-a=1\\4a+3b=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=-1\\b=2\end{matrix}\right.\)
=> f(x)=-x+2
f(-1)=3