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If two distinct non-zero real variables \(x\) and \(y\) are such that \((x + y)\) is proportional to \((x - y)\) then the value of \(\frac{x}{y}\)

  • A.depends on \(xy\)
  • B.depends only on \(x\) and not on \(y\)
  • C.depends only on \(y\) and not on \(x\)
  • D.is a constant

Answer: D

The ratio \(\frac{x}{y}\) is a constant.

Proportionality means \(x + y = k(x - y)\) for a fixed constant \(k\). Collect the terms:

\[ \begin{aligned} x + y &= kx - ky \\ y(1 + k) &= x(k - 1) \\ \frac{x}{y} &= \frac{k + 1}{k - 1} \end{aligned} \]

The right-hand side contains only \(k\), so \(x/y\) has the same value whatever \(x\) and \(y\) are, provided they satisfy the proportionality. (\(k = 1\) would force \(y = 0\), which the question excludes.) It does not depend on \(xy\), on \(x\) alone or on \(y\) alone.

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