Question:

If \( x = 5 + 2\sec \theta \) and \( y = 5 + 2\tan \theta \), then \( (x-5)^2 - (y-5)^2 \) is equal to

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Always reduce expressions to standard trigonometric identities before simplifying.
Updated On: May 8, 2026
  • \(3\)
  • \(1\)
  • \(0\)
  • \(4\)
  • \(2\)
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The Correct Option is D

Solution and Explanation

Concept: Use identity: \[ \sec^2 \theta - \tan^2 \theta = 1 \]

Step 1: Rewrite expression

\[ (x-5)^2 = (2\sec \theta)^2 = 4\sec^2 \theta \] \[ (y-5)^2 = (2\tan \theta)^2 = 4\tan^2 \theta \]

Step 2: Substitute

\[ (x-5)^2 - (y-5)^2 = 4\sec^2 \theta - 4\tan^2 \theta \]

Step 3: Factor out 4

\[ = 4(\sec^2 \theta - \tan^2 \theta) \]

Step 4: Apply identity

\[ \sec^2 \theta - \tan^2 \theta = 1 \]

Step 5: Final result

\[ = 4 \cdot 1 = 4 \] \[ \boxed{4} \]
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