I'm reviewing my notes and i can't understand this part:(adsbygoogle = window.adsbygoogle || []).push({});

http://s1.ipicture.ru/uploads/20111202/OlsTV2UV.jpg

I have enclosed each corresponding term in the same coloured box. I've reviewed this solved example several times now but can't figure out how the result was obtained in the last line. I expanded each term (D^2 - 3D)/5 according to its power but ended up with terms exceeding powers of 3.

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# Homework Help: D-operator homework help

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