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Question

If \(\alpha\) and \(\beta\) are complementary angles such that \(\alpha - \beta = \frac{\pi}{6}\) and \(m \tan \beta = n \tan \alpha\), then what is \(\left( \frac{m+n}{m-n} \right)\) equal to ?

This question was previously asked in
NDA 1 2026 GAT Question Paper (12-Apr-2026)
The correct answer is

2

To solve the problem, we need to analyze the given conditions: the angles \(\alpha\)and \(\beta\) are complementary, which means they satisfy:

  • \(\alpha + \beta = \frac{\pi}{2}\)

We are also given that:

  • \(\alpha - \beta = \frac{\pi}{6}\)

Now, let's solve these equations. Add the two equations:

  • \(\alpha + \beta + \alpha - \beta = \frac{\pi}{2} + \frac{\pi}{6}\)

This simplifies to:

  • \(2\alpha = \frac{\pi}{2} + \frac{\pi}{6}\)

Simplifying the right side:

  • \(\frac{\pi}{2} = \frac{3\pi}{6}\) and so:
  • \(2\alpha = \frac{3\pi}{6} + \frac{\pi}{6} = \frac{4\pi}{6} = \frac{2\pi}{3}\)

Dividing by 2:

  • \(\alpha = \frac{\pi}{3}\)

Using \(\alpha + \beta = \frac{\pi}{2}\), substitute for \(\alpha\):

  • \(\frac{\pi}{3} + \beta = \frac{\pi}{2}\)

Thus:

  • \(\beta = \frac{\pi}{2} - \frac{\pi}{3} = \frac{3\pi}{6} - \frac{2\pi}{6} = \frac{\pi}{6}\)

Now, we know:

  • \(\alpha = \frac{\pi}{3}\)
  • \(\beta = \frac{\pi}{6}\)

The problem also states that \(m \tan \beta = n \tan \alpha\). So, substitute the known values of \(\alpha\) and \(\beta\):

  • \(m \tan\left(\frac{\pi}{6}\right) = n \tan\left(\frac{\pi}{3}\right)\)

Further simplifying, we use the known values:

  • \(\tan\left(\frac{\pi}{6}\right) = \frac{1}{\sqrt{3}}\)
  • \(\tan\left(\frac{\pi}{3}\right) = \sqrt{3}\)

Thus, the equation becomes:

  • \(m \cdot \frac{1}{\sqrt{3}} = n \cdot \sqrt{3}\)
  • \(\frac{m}{\sqrt{3}} = n \sqrt{3}\)

Cross-multiplying gives:

  • \(m = n \cdot 3\)

Now we substitute this relation into the expression we need to evaluate:

  • \(\frac{m+n}{m-n} = \frac{3n + n}{3n - n} = \frac{4n}{2n} = 2\)

The correct answer is thus 2.

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