Изменения

<center>

<tex>\dfrac{1}{1+z}=\sum_{n=0}^\infty a_n x^n </tex>

<tex>\dfrac{7}{(1-z)^2}=\sum_{n=0}^\infty a_n x^n </tex>

<tex>\dfrac{z}{(1-z)^2}=\sum_{n=0}^\infty a_n x^n .</tex>

</center>