In the calculation, F2n=Fn−1Fn+FnFn+1 =(Fn+1–Fn)Fn+FnFn+1 =FnFn+1–F2n+"FnFn−1" =2Fn+1Fn–F2n
in third line, it is FnFn+1
In the calculation, F2n=Fn−1Fn+FnFn+1 =(Fn+1–Fn)Fn+FnFn+1 =FnFn+1–F2n+"FnFn−1" =2Fn+1Fn–F2n
in third line, it is FnFn+1