Question:medium

If $\alpha$ and $\beta$ are acute angles such that $\alpha + \beta$ and $\alpha - \beta$ satisfy the equation $\tan^2 \theta - 4\tan \theta + 1 = 0$, then $\alpha$ and $\beta$ are respectively

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Memorizing the trigonometric values for non-standard but common angles like $15^\circ$ and $75^\circ$ ($\tan 15^\circ = 2 - \sqrt{3}$, $\tan 75^\circ = 2 + \sqrt{3}$) can significantly speed up solving such problems.
Updated On: Apr 29, 2026
  • $45^\circ, 30^\circ$
  • $75^\circ, 15^\circ$
  • $30^\circ, 60^\circ$
  • $60^\circ, 45^\circ$
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The Correct Option is A

Solution and Explanation

To solve the given problem, we need to find the values of the acute angles \( \alpha \) and \( \beta \) using the condition that \( \alpha + \beta \) and \( \alpha - \beta \) satisfy the equation:

\(\tan^2 \theta - 4\tan \theta + 1 = 0\)

Firstly, let's solve the quadratic equation \(\tan^2 \theta - 4\tan \theta + 1 = 0\):

The equation is of the form \(ax^2 + bx + c = 0\), where \( a = 1 \), \( b = -4 \), and \( c = 1 \).

The quadratic formula is given by:

\(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\)

Substitute the values of \( a \), \( b \), and \( c \):

\(x = \frac{-(-4) \pm \sqrt{(-4)^2 - 4 \cdot 1 \cdot 1}}{2 \cdot 1}\)

This simplifies to:

\(x = \frac{4 \pm \sqrt{16 - 4}}{2} = \frac{4 \pm \sqrt{12}}{2} = \frac{4 \pm 2\sqrt{3}}{2}\)

\(x = 2 \pm \sqrt{3}\)

Thus, the solutions to the quadratic equation are:

\(\tan \theta = 2 + \sqrt{3}\) and \(\tan \theta = 2 - \sqrt{3}\)

Now, we know the values of \(\tan(\alpha + \beta)\) and \(\tan(\alpha - \beta)\) must satisfy these values. We need to check which angles \(\alpha\) and \(\beta\) will satisfy these conditions.

We use the known tangent values for certain special angles:

\(\tan 75^\circ = 2 + \sqrt{3}\)

\(\tan 15^\circ = 2 - \sqrt{3}\)

This means \(\alpha + \beta = 75^\circ\) and \(\alpha - \beta = 15^\circ\).

We can find \(\alpha\) and \(\beta\) by solving the system of equations:

  • \(\alpha + \beta = 75^\circ\)
  • \(\alpha - \beta = 15^\circ\)

Adding these two equations, we get:

\(2\alpha = 90^\circ \implies \alpha = 45^\circ\)

Substituting \(\alpha = 45^\circ\) into the first equation:

\(45^\circ + \beta = 75^\circ \implies \beta = 30^\circ\)

Therefore, the values of \(\alpha\) and \(\beta\) that satisfy the given conditions are \(45^\circ\) and \(30^\circ\) respectively.

The correct answer is: \(45^\circ, 30^\circ\)

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