Question:

The origin is shifted to (2, 3) and axes are rotated through angle \(\theta\). If \(3x^2+2xy+3y^2-18x-22y+50=0\) transforms to \(4x^2+2y^2-1=0\), then \(\theta =\)

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If \(A=C\) in \(Ax^2+Bxy+Cy^2\), then immediately \(\theta=\frac{\pi}{4}\).
Updated On: Jun 9, 2026
  • \(\frac{\pi}{4}\)
  • \(\frac{\pi}{6}\)
  • \(\frac{\pi}{3}\)
  • \(\frac{\pi}{2}\)
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The Correct Option is A

Solution and Explanation

Concept: For a second-degree equation \[ Ax^2+Bxy+Cy^2+Dx+Ey+F=0, \] the angle of rotation required to eliminate the \(xy\)-term is given by \[ \tan 2\theta=\frac{B}{A-C}. \]

Step 1: Identify the coefficients of the quadratic terms. Given \[ 3x^2+2xy+3y^2-18x-22y+50=0 \] Comparing with \[ Ax^2+Bxy+Cy^2+Dx+Ey+F=0, \] we obtain \[ A=3,\qquad B=2,\qquad C=3. \]

Step 2: Apply the rotation formula. Using \[ \tan 2\theta = \frac{B}{A-C} \] gives \[ \tan 2\theta = \frac{2}{3-3} = \infty \] Hence \[ 2\theta=\frac{\pi}{2} \]

Step 3: Find \(\theta\). \[ \theta=\frac{\pi}{4} \] Therefore, \[ \boxed{\theta=\frac{\pi}{4}} \]
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