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Mathematics

Solve the following simultaneous equations:

3x+y+2xy=3,  2x+y+3xy=113\dfrac{3}{x + y} + \dfrac{2}{x - y} = 3,\;\dfrac{2}{x + y} + \dfrac{3}{x - y} = \dfrac{11}{3}

Linear Equations

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Answer

Given,

Equations:

3x+y+2xy=3\dfrac{3}{x + y} + \dfrac{2}{x - y} = 3 ……..(1)

2x+y+3xy=113\dfrac{2}{x + y} + \dfrac{3}{x - y} = \dfrac{11}{3} ……….(2)

Multiplying equation (1) by 2, we get:

2(3x+y+2xy)=3×2(6x+y+4xy)=6 ………(3) \Rightarrow 2\Big(\dfrac{3}{x + y} + \dfrac{2}{x - y}\Big) = 3 \times 2 \\[1em] \Rightarrow \Big(\dfrac{6}{x + y} + \dfrac{4}{x - y}\Big) = 6 \text{ ………(3) }

Multiplying equation (2) by 3, we get:

3(2x+y+3xy)=113×3(6x+y+9xy)=11 ………(4) \Rightarrow 3\Big(\dfrac{2}{x + y} + \dfrac{3}{x - y}\Big) = \dfrac{11}{3} \times 3 \\[1em] \Rightarrow \Big(\dfrac{6}{x + y} + \dfrac{9}{x - y}\Big) = 11 \text{ ………(4) }

Subtracting equation (3) from (4), we get:

(6x+y+9xy)(6x+y+4xy)=116(6x+y+9xy6x+y4xy)=5(9xy4xy)=5(5xy)=55=5(xy)xy=1 ………(5) \Rightarrow \Big(\dfrac{6}{x + y} + \dfrac{9}{x - y}\Big) - \Big(\dfrac{6}{x + y} + \dfrac{4}{x - y}\Big) = 11 - 6 \\[1em] \Rightarrow \Big(\dfrac{6}{x + y} + \dfrac{9}{x - y} - \dfrac{6}{x + y} - \dfrac{4}{x - y}\Big) = 5 \\[1em] \Rightarrow \Big(\dfrac{9}{x - y} - \dfrac{4}{x - y}\Big) = 5 \\[1em] \Rightarrow \Big(\dfrac{5}{x - y}\Big) = 5 \\[1em] \Rightarrow 5 = 5(x - y) \\[1em] \Rightarrow x - y = 1 \text{ ………(5) }

Substituting value of x - y from equation (5) in equation (1), we get:

3x+y+21=33x+y+2=33x+y=323x+y=1x+y=3 ………(6) \Rightarrow \dfrac{3}{x + y} + \dfrac{2}{1} = 3 \\[1em] \Rightarrow \dfrac{3}{x + y} + 2 = 3 \\[1em] \Rightarrow \dfrac{3}{x + y} = 3 - 2 \\[1em] \Rightarrow \dfrac{3}{x + y} = 1 \\[1em] \Rightarrow x + y = 3 \text{ ………(6) }

Adding equations (5) and (6), we get:

x+y+xy=3+12x=4x=42=2.\Rightarrow x + y + x - y = 3 + 1 \\[1em] \Rightarrow 2x = 4 \\[1em] \Rightarrow x = \dfrac{4}{2} = 2.

Substituting value of x in equation (6), we get:

⇒ x + y = 3

⇒ 2 + y = 3

⇒ y = 3 - 2

⇒ y = 1.

Hence, x = 2, y = 1.

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