<s>[INST] Best way to expand $(2+x-x^2)^6$ 
I've completed part $(a)$ and gotten:
$64+192y+240y^2+160y^3+...$
Using intuition I substituted $x-x^2$ for $y$ and started listing the values for :
$y, y^2 $ and $y^3,$ in terms of $x$.
$y=(x-x^2)\\y^2=(x-x^2)^2 = x^2-2x^3+x^4;\\y^3 = (x-x^2)^3 = (x-x^2)(x^2-2x^3+x^4) = \;...$
Everything became complicated before I had even started to substitute these new-found values back into the polynomial devised from part $(a)$; for a 3 - out of 75 - mark question this seems extremely over-complicated. Am I doing it inefficiently / incorrectly; is there a pre-defined or easier method; or is it simple expansion and substitution that I'm too lazy to complete?
 [/INST] I think I would say
$((x+2)(x-1))^6 = (x+2)^6(x-1)^6\\
(64 + 192x + 240x^2 + 160x^3 ...)(1 - 6x + 15x^2 - 20x^3 ...)$
I don't care about any powers bigger than 3
$64 + (64(-6) + 192)x + (64*15+192(-6) + 240)x^2 + (64(-20)+ 192*15 + 240*(-6) + 160)x^3...\\
64 - 192 x + 48 x^2 + 320x^3...$
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