Question:
Factorise
$(x+1)^{3}+(x-1)^{3}$
Solution:
$(x+1)^{3}+(x-1)^{3}$
$=(x+1+x-1)\left[(x+1)^{2}+(x-1)^{2}-(x-1)(x+1)\right]$
$=(2 x)\left[(x+1)^{2}+(x-1)^{2}-\left(x^{2}-1\right)\right]$
$=2 x\left(x^{2}+1+2 x+x^{2}+1-2 x-x^{2}+1\right)$
$=2 x\left(x^{2}+3\right)$
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