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cn+2=cn+1+2cnc_{n+2}=c_{n+1}+2c_ncn+2=cn+1+2cn
[anbncndn][01]=[bn+1dn+1]\begin{bmatrix}a_n&b_n\\c_n&d_n\end{bmatrix}\begin{bmatrix}0\\1\end{bmatrix}=\begin{bmatrix}b_{n+1}\\d_{n+1}\end{bmatrix}[ancnbndn][01]=[bn+1dn+1]
d2n−a2n=(dn)2−(an)2d_{2n}-a_{2n}=(d_n)^2-(a_n)^2d2n−a2n=(dn)2−(an)2