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Mathematics

Solution of equations x7y2=2 and xy3=3\dfrac{x}{7} - \dfrac{y}{2} = 2 \text{ and } \dfrac{x - y}{3} = 3 is :

  1. x = 7, y = 2

  2. x = -7, y = 2

  3. x = -7, y = -2

  4. x = 7, y = -2

Linear Equations

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Answer

Given, equations : x7y2=2 and xy3=3\dfrac{x}{7} - \dfrac{y}{2} = 2 \text{ and } \dfrac{x - y}{3} = 3

Simplifying first equation :

x7y2=22x7y14=22x7y=282x7y28=0 ……..(1)\Rightarrow \dfrac{x}{7} - \dfrac{y}{2} = 2 \\[1em] \Rightarrow \dfrac{2x - 7y}{14} = 2 \\[1em] \Rightarrow 2x - 7y = 28 \\[1em] \Rightarrow 2x - 7y - 28 = 0 \text{ ……..(1)}

Simplifying second equation :

xy3=3xy=9xy9=0 …….(2)\Rightarrow \dfrac{x - y}{3} = 3 \\[1em] \Rightarrow x - y = 9 \\[1em] \Rightarrow x - y - 9 = 0 \text{ …….(2)}

By cross-multiplication method :

x(7)×(9)(1)×(28)=y(28)×1(9)×2=12×(1)1×(7)x6328=y28(18)=12+7x35=y10=15x35=15 and y10=15x=355 and y=105x=7 and y=2.\Rightarrow \dfrac{x}{(-7) \times (-9) - (-1) \times (-28)} = \dfrac{y}{(-28) \times 1 - (-9) \times 2} = \dfrac{1}{2 \times (-1) - 1 \times (-7)} \\[1em] \Rightarrow \dfrac{x}{63 - 28} = \dfrac{y}{-28 - (-18)} = \dfrac{1}{-2 + 7} \\[1em] \Rightarrow \dfrac{x}{35} = \dfrac{y}{-10} = \dfrac{1}{5} \\[1em] \Rightarrow \dfrac{x}{35} = \dfrac{1}{5} \text{ and } \dfrac{y}{-10} = \dfrac{1}{5} \\[1em] \Rightarrow x = \dfrac{35}{5} \text{ and } y = \dfrac{-10}{5} \\[1em] \Rightarrow x = 7 \text{ and } y = -2.

Hence, Option 4 is the correct option.

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