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Mathematics

Rationalize the denominators of:

(i) 235\dfrac{2\sqrt{3}}{\sqrt{5}}

(ii) 656+5\dfrac{\sqrt{6} - \sqrt{5}}{\sqrt{6} + \sqrt{5}}

Rational Irrational Nos

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Answer

(i) Given,

235\dfrac{2\sqrt{3}}{\sqrt{5}}

Let us rationalise the denominator,

23×55×5215(5)22155\Rightarrow \dfrac{2\sqrt{3} \times \sqrt{5}}{\sqrt{5} \times \sqrt{5}} \\[1em] \Rightarrow \dfrac{2\sqrt{15}}{(\sqrt{5})^2}\\[1em] \Rightarrow \dfrac{2\sqrt{15}}{5}

Hence,235=2155\dfrac{2\sqrt{3}}{\sqrt{5}} = \dfrac{2\sqrt{15}}{5}

(ii) Given, 656+5\dfrac{\sqrt{6} - \sqrt{5}}{\sqrt{6} + \sqrt{5}}

Let us rationalise the denominator,

(65)×(65)(6+5)×(65)=(65)2(6)2(5)2=(6)2+(5)22×6×565=6+52×301=11230\Rightarrow \dfrac{(\sqrt{6} - \sqrt{5}) \times (\sqrt{6} - \sqrt{5})}{(\sqrt{6} + \sqrt{5})\times (\sqrt{6} - \sqrt{5})}\\[1em] = \dfrac{(\sqrt{6} - \sqrt{5})^2}{(\sqrt{6})^2 - (\sqrt{5})^2}\\[1em] = \dfrac{(\sqrt{6})^2 + (\sqrt{5})^2 - 2 \times \sqrt{6} \times \sqrt{5}}{6 - 5}\\[1em] = \dfrac{6 + 5 - 2 \times \sqrt{30}}{1}\\[1em] = 11 - 2\sqrt{30}

Hence, 656+5=11230\dfrac{\sqrt{6} - \sqrt{5}}{\sqrt{6} + \sqrt{5}} = 11 - 2\sqrt{30}.

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