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Mathematics

Solve the following pair of equations:

23(2xy)+12(x+2y)=512,12xy2x+2y=16\dfrac{2}{3(2x - y)} + \dfrac{1}{2(x + 2y)} = \dfrac{5}{12}, \dfrac{1}{2x - y} - \dfrac{2}{x + 2y} = \dfrac{1}{6}

Linear Equations

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Answer

Substituting 12xy\dfrac{1}{2x - y} = a and 1x+2y\dfrac{1}{x + 2y} = b in above equations, we get :

23a+12b=512\dfrac{2}{3}a + \dfrac{1}{2}b = \dfrac{5}{12} ……….(1)

⇒ a - 2b = 16\dfrac{1}{6} ………(2)

Multiplying equation (1) by 32\dfrac{3}{2} we get :

32(23a+12b)=32×512a+34b=58 ………..(3)\Rightarrow \dfrac{3}{2}\Big(\dfrac{2}{3}a + \dfrac{1}{2}b\Big) = \dfrac{3}{2} \times \dfrac{5}{12} \\[1em] \Rightarrow a + \dfrac{3}{4}b = \dfrac{5}{8} \text{ ………..(3)}

Subtracting equation (2) from (3), we get :

a+34b(a2b)=5816aa+34b+2b=154243b+8b4=112411b4=1124b=1124×411=16.1x+2y=16x+2y=6x=62y …………(4)\Rightarrow a + \dfrac{3}{4}b - (a - 2b) = \dfrac{5}{8} - \dfrac{1}{6} \\[1em] \Rightarrow a - a + \dfrac{3}{4}b + 2b = \dfrac{15 - 4}{24} \\[1em] \Rightarrow \dfrac{3b + 8b}{4} = \dfrac{11}{24} \\[1em] \Rightarrow \dfrac{11b}{4} = \dfrac{11}{24} \\[1em] \Rightarrow b = \dfrac{11}{24} \times \dfrac{4}{11} = \dfrac{1}{6}. \\[1em] \therefore \dfrac{1}{x + 2y} = \dfrac{1}{6} \\[1em] \Rightarrow x + 2y = 6 \\[1em] \Rightarrow x = 6 - 2y \text{ …………(4)}

Substituting b = 16\dfrac{1}{6} in equation (2), we get :

a2×16=16a13=16a=16+13a=1+26a=36a=1212xy=122xy=2 ……(5)\Rightarrow a - 2 \times \dfrac{1}{6} = \dfrac{1}{6} \\[1em] \Rightarrow a - \dfrac{1}{3} = \dfrac{1}{6} \\[1em] \Rightarrow a = \dfrac{1}{6} + \dfrac{1}{3} \\[1em] \Rightarrow a = \dfrac{1 + 2}{6} \\[1em] \Rightarrow a = \dfrac{3}{6} \\[1em] \Rightarrow a = \dfrac{1}{2} \\[1em] \therefore \dfrac{1}{2x - y} = \dfrac{1}{2}\\[1em] \Rightarrow 2x - y = 2 \text{ ……(5)}

Substituting value of x from equation (4) in (5), we get :

⇒ 2(6 - 2y) - y = 2

⇒ 12 - 4y - y = 2

⇒ 12 - 5y = 2

⇒ -5y = 2 - 12

⇒ -5y = -10

⇒ y = 105\dfrac{-10}{-5} = 2.

Substituting y = 2 in equation (4), we get :

⇒ x = 6 - 2y

⇒ x = 6 - 2(2) = 6 - 4 = 2.

Hence, x = 2 and y = 2.

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