Rationalise the denominator in each of the following:
$\frac{1}{7-4 \sqrt{3}}$
$\frac{1}{7-4 \sqrt{3}}$
(A) To rationalise the denominator of $\frac{1}{7-4 \sqrt{3}}$,we multiply the numerator and the denominator by the conjugate of the denominator,which is $7+4 \sqrt{3}$.
$\frac{1}{7-4 \sqrt{3}} \times \frac{7+4 \sqrt{3}}{7+4 \sqrt{3}} = \frac{7+4 \sqrt{3}}{(7)^2 - (4 \sqrt{3})^2}$
$= \frac{7+4 \sqrt{3}}{49 - (16 \times 3)}$
$= \frac{7+4 \sqrt{3}}{49 - 48}$
$= \frac{7+4 \sqrt{3}}{1}$
$= 7+4 \sqrt{3}$
$\frac{1}{7-4 \sqrt{3}} \times \frac{7+4 \sqrt{3}}{7+4 \sqrt{3}} = \frac{7+4 \sqrt{3}}{(7)^2 - (4 \sqrt{3})^2}$
$= \frac{7+4 \sqrt{3}}{49 - (16 \times 3)}$
$= \frac{7+4 \sqrt{3}}{49 - 48}$
$= \frac{7+4 \sqrt{3}}{1}$
$= 7+4 \sqrt{3}$
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