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Question

If $\tan\theta = \frac{7}{8}$, then evaluate $\frac{(1 + \sin\theta)(1 - \sin\theta)}{(1 + \cos\theta)(1 - \cos\theta)(\cot\theta)}$:

The correct answer is
$\frac{8}{7}$

Given:

tanθ = 7/8

⇒ Assume in a right triangle:

height = 7, base = 8, hypotenuse = √113

sinθ = 7/√113, cosθ = 8/√113, cotθ = 8/7

Now the expression:

[(1 + sinθ)(1 − sinθ)] / [(1 + cosθ)(1 − cosθ)(cotθ)]

= (1 − sin²θ) / [(1 − cos²θ)(cotθ)]

= cos²θ / [sin²θ · cotθ]

= cos²θ / [sin²θ · (cosθ/sinθ)]

= cos²θ / (sinθ cosθ)

= cosθ / sinθ

= cotθ

= 8/7

Thus the answer = 8/7

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Important Questions from Trigonometric Identities

  1. If cos 2θ = sin θ and θ lies between 0 and 90°, then θ will be:

  2. \(\frac{3 - 4\sin^2 \theta}{\cos^2 \theta} + 2\tan^2 \theta\) can be simplified as:

  3. Simplify \( \left(\frac{1}{\sin^2 A} - 1\right) \), where \( 0 < A \leq 90^\circ \).

  4. If \( \tan \theta = \frac{8}{15} \), then the value of \( \sqrt{\frac{1 - \sin \theta}{1 + \sin \theta}} \) is:

  5. If the volume of a cuboid is \(3x^2 - 27\), then its possible dimensions are:

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