Factorize each of the following expression:
(2x + 1)2 − 9x4
$(2 \mathrm{x}+1)^{2}-9 \mathrm{x}^{4}$
$=(2 \mathrm{x}+1)^{2}-\left(3 \mathrm{x}^{2}\right)^{2}$
$=\left[(2 \mathrm{x}+1)-3 \mathrm{x}^{2}\right]\left[(2 \mathrm{x}+1)+3 \mathrm{x}^{2}\right]$
$=\left(-3 \mathrm{x}^{2}+2 \mathrm{x}+1\right)\left(3 \mathrm{x}^{2}+2 \mathrm{x}+1\right)$
We can factorise the quadratic expressions in the curved brackets as:
$\left(-3 \mathrm{x}^{2}+3 \mathrm{x}-\mathrm{x}+1\right)\left(3 \mathrm{x}^{2}+2 \mathrm{x}+1\right)$
$=\{3 \mathrm{x}(-\mathrm{x}+1)+1(-\mathrm{x}+1)\}\left(3 \mathrm{x}^{2}+2 \mathrm{x}+1\right)$
$=(-\mathrm{x}+1)(3 \mathrm{x}+1)\left(3 \mathrm{x}^{2}+2 \mathrm{x}+1\right)$
$=-(\mathrm{x}-1)(3 \mathrm{x}+1)\left(3 \mathrm{x}^{2}+2 \mathrm{x}+1\right)$
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