Vă rog!!!!!!!!!!!!!!!!!!!!

Răspuns:
f(1)=1+1=2
f(2)=2+1=3
f(3)=3+1=4
f(1)+f(3)=2+4=6}
2•f(2)=2•3=6 }=>
=>f(1)+f(3)=2•f(2)