You might need
f(1) = 1
f(2)= 2
(f(n) = f(n − 2) + f(n-1)
f(3) =

“exterior angles of triangles. an exterior (or external) angle is the angle between one side of a triangle and the extension of an adjacent side. try this drag the orange dots on any vertex to reshape the triangle.” look to get to the answer i explained what it means and other things i hope it you .