Q.If \((3x - 2y) : (3x + 2y) = 4 : 5\), then what is the value of \((x + y) : (x - y)\)?

Given: \((3x - 2y) : (3x + 2y) = 4 : 5\) Or, \(\frac{3x - 2y}{3x + 2y} = \frac{4}{5}\)
Now, apply componendo and dividendo: \[ \frac{(3x - 2y) + (3x + 2y)}{(3x - 2y) - (3x + 2y)} = \frac{4 + 5}{4 - 5} \] \[ \Rightarrow \frac{6x}{-4y} = \frac{9}{-1} \] \[ \Rightarrow \frac{x}{y} = \frac{9 \times (-4)}{-1 \times 6} = \frac{36}{6} = 6 \] Using componendo and dividendo again: \[ \frac{x + y}{x - y} = \frac{6 + 1}{6 - 1} = \frac{7}{5} \] \[ \therefore (x + y) : (x - y) = 7 : 5 \]
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