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Mathematics

If 3x+2x13x2x1=5\dfrac{\sqrt{3x} + \sqrt{2x - 1}}{\sqrt{3x} - \sqrt{2x - 1}} = 5, prove that x = 32\dfrac{3}{2}.

Ratio Proportion

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Answer

(i) Given,

3x+2x13x2x1=5\dfrac{\sqrt{3x} + \sqrt{2x - 1}}{\sqrt{3x} - \sqrt{2x - 1}} = 5

Applying Componendo and Dividendo, we get :

3x+2x1+3x2x13x+2x1(3x2x1)=5+15123x3x+2x13x+2x1=6423x22x1=323x2x1=32\Rightarrow \dfrac{\sqrt{3x} + \sqrt{2x - 1} + \sqrt{3x} - \sqrt{2x - 1}}{\sqrt{3x} + \sqrt{2x - 1} - (\sqrt{3x} - \sqrt{2x - 1})} = \dfrac{5 + 1}{5 - 1} \\[1em] \Rightarrow \dfrac{2\sqrt{3x}}{\sqrt{3x} + \sqrt{2x - 1} - \sqrt{3x} + \sqrt{2x - 1}} = \dfrac{6}{4} \\[1em] \Rightarrow \dfrac{2\sqrt{3x}}{2 \sqrt{2x - 1}} = \dfrac{3}{2} \\[1em] \Rightarrow \dfrac{\sqrt{3x}}{ \sqrt{2x - 1}} = \dfrac{3}{2}

Squaring both sides, we get :

(3x2x1)2=(32)2(3x2x1)=(94)4(3x)=9(2x1)12x=18x918x12x=96x=9x=96=32\Rightarrow \Big(\dfrac{\sqrt{3x}}{ \sqrt{2x - 1}}\Big)^2 = \Big(\dfrac{3}{2}\Big)^2 \\[1em] \Rightarrow \Big(\dfrac{3x}{2x - 1}\Big) = \Big(\dfrac{9}{4}\Big) \\[1em] \Rightarrow 4(3x) = 9(2x - 1) \\[1em] \Rightarrow 12x = 18x - 9 \\[1em] \Rightarrow 18x - 12x = 9 \\[1em] \Rightarrow 6x = 9 \\[1em] \Rightarrow x = \dfrac{9}{6} = \dfrac{3}{2}

Hence, proved that x = 32\dfrac{3}{2}.

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