Question
Use the direct method to evaluate : $\left(\mathrm{z}-\frac{2}{3}\right)\left(\mathrm{z}+\frac{2}{3}\right)$
✓
Answer
Note : $(a+b)(a-b)=a^2-b^2$
$\left(z-\frac{2}{3}\right)\left(z+\frac{2}{3}\right)=(z)^2-\left(\frac{2}{3}\right)^2$
$ =z^2-\frac{4}{9}$
$\left(z-\frac{2}{3}\right)\left(z+\frac{2}{3}\right)=(z)^2-\left(\frac{2}{3}\right)^2$
$ =z^2-\frac{4}{9}$
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