1. The problem statement, all variables and given/known data *refer to attached drawing* 2. Relevant equations *refer to attached drawing* 3. The attempt at a solution Basically i dont understand how (x+4) exponent of 3 disappeared in the simplfication. My attempts at solution were trying to expand the brackets and seeing if i could figure it out that way but i still couldn't. Could someone please look at the attached picture and explain to me how that simplication occured. Or if you can not do that could you please tell me which chapters of my book i must read in order to understand it (my book covers all chapters of mathematics, so just tell me the relevant mathemathic topics please) Greatly appreciated if someone could help us out.