All Exams Test series for 1 year @ ₹349 only
Question

If \(\frac{\sin \theta - \cos \theta + 1}{\sin \theta + \cos \theta - 1} = p \sec \theta + q \tan \theta\), where \(0 < \theta < \frac{\pi}{2}\), then what is \(p + q\) equal to?

This question was previously asked in
CDS 2 2024 Maths Question Paper (01-Sep-2024)
The correct answer is
2

Simplify Trigonometric Expression

We are given the equation: \( \frac{\sin \theta - \cos \theta + 1}{\sin \theta + \cos \theta - 1} = p \sec \theta + q \tan \theta \) Our goal is to simplify the left-hand side (LHS) of the equation.

First, let's rearrange the terms in the numerator and the denominator:

\( \text{LHS} = \frac{(1 + \sin \theta) - \cos \theta}{(\sin \theta - 1) + \cos \theta} \)

To simplify this expression, we can divide both the numerator and the denominator by \(\cos \theta\) (since \(0 < \theta < \frac{\pi}{2}\), \(\cos \theta \neq 0\)):

\( \text{LHS} = \frac{\frac{1}{\cos \theta} + \frac{\sin \theta}{\cos \theta} - \frac{\cos \theta}{\cos \theta}}{\frac{\sin \theta}{\cos \theta} + \frac{\cos \theta}{\cos \theta} - \frac{1}{\cos \theta}} \)

Using the identities \(\sec \theta = \frac{1}{\cos \theta}\) and \(\tan \theta = \frac{\sin \theta}{\cos \theta}\), we get:

\( \text{LHS} = \frac{\sec \theta + \tan \theta - 1}{\tan \theta + 1 - \sec \theta} \)

Now, let's rearrange the terms again:

\( \text{LHS} = \frac{(\sec \theta + \tan \theta) - 1}{1 - \sec \theta + \tan \theta} \)

We can use the trigonometric identity \(1 = \sec^2 \theta - \tan^2 \theta\). Substitute this into the numerator:

\( \text{LHS} = \frac{\sec \theta + \tan \theta - (\sec^2 \theta - \tan^2 \theta)}{\tan \theta + 1 - \sec \theta} \)

Factor the difference of squares term \(\sec^2 \theta - \tan^2 \theta = (\sec \theta - \tan \theta)(\sec \theta + \tan \theta)\):

\( \text{LHS} = \frac{(\sec \theta + \tan \theta) - (\sec \theta - \tan \theta)(\sec \theta + \tan \theta)}{\tan \theta + 1 - \sec \theta} \)

Factor out \((\sec \theta + \tan \theta)\) from the numerator:

\( \text{LHS} = \frac{(\sec \theta + \tan \theta) [1 - (\sec \theta - \tan \theta)]}{\tan \theta + 1 - \sec \theta} \) \( \text{LHS} = \frac{(\sec \theta + \tan \theta) (1 - \sec \theta + \tan \theta)}{\tan \theta + 1 - \sec \theta} \)

Notice that the term \((1 - \sec \theta + \tan \theta)\) is the same as \((\tan \theta + 1 - \sec \theta)\). Since \(0 < \theta < \frac{\pi}{2}\), the denominator \(\tan \theta + 1 - \sec \theta\) is not zero. Thus, we can cancel this term from the numerator and denominator:

\( \text{LHS} = \sec \theta + \tan \theta \)

Equate and Compare Coefficients

Now, we equate the simplified LHS with the given right-hand side (RHS):

\( \sec \theta + \tan \theta = p \sec \theta + q \tan \theta \)

For this equation to hold true for all \(\theta\) in the specified range, the coefficients of \(\sec \theta\) and \(\tan \theta\) on both sides must be equal.

  • Comparing the coefficients of \(\sec \theta\): \(1 = p\)
  • Comparing the coefficients of \(\tan \theta\): \(1 = q\)

Calculate the Final Value

We found that \(p = 1\) and \(q = 1\). The question asks for the value of \(p + q\).

\( p + q = 1 + 1 = 2 \)

Therefore, the value of \(p + q\) is 2.

Was this answer helpful?

Similar Questions

  1. If sinθ = (m 2– n 2)/(m 2+ n 2) and 0 < θ < π/2, then what is the value of cosθ?

  2. What is \((\sec\theta - \tan\theta) - \frac{1-\sin\theta}{1+\sin\theta}\) equal to?
  3. If \(\cot\theta = \sqrt{7}\), then what is \(\frac{\text{cosec}^2\theta-\sec^2\theta}{\text{cosec}^2\theta+\sec^2\theta}\) equal to?
  4. What is \((p\sin\theta + q\cos\theta)\) equal to?
  5. What is \(p^2q^2 (p^2 + q^2+3)\) equal to?
  6. What is sin 4θ - cos 4θ equal to for any real number θ?

  7. What is cot 1° cot 23° cot 45° cot 67° cot 89° equal to?

  8. Consider the following statements:

    1. (sec 2θ - 1) (1 - cosec 2θ) = 1

    2. sin θ (1 + cos θ) -1 + (1 + cos θ) (sin θ) -1 = 2 cosec θ

    Which of the above is/are correct?
  9. If sec x cosec x = 2, then what is the tan nx + cot nx equal to?

  10. If \(3 \sin \theta + 5 \cos \theta = 5\), then what is the value of \(5 \sin \theta - 3 \cos \theta\)?

Important Questions from Trigonometric Identities

  1. What is \(\rm \frac{1+tan^2\theta}{1+cot^2\theta}-\left(\frac{1-tan\theta}{1-cot\theta}\right)^2\) equal to?

  2. If 3sin θ + 5cos θ = 5, then the value of 5sin θ - 3cos θ is equal to: 

  3. If angle C of a triangle ABC is a right angle where a, b and c are the sides opposite to the angles A, B and C respectively then what is tan A + tan B equal to?

  4. If \(\sin \left( {A - B} \right) = \frac{1}{2}\)  and  \(\cos \left( {A + B} \right) = \frac{1}{2}\) , where A > B > 0° and A + B is an acute angle, then the value of A is:

  5. Find the value of $\cos 10^\circ \times \cos 30^\circ \times \cos 50^\circ \times \cos 70^\circ$

Need Expert Advice?
Test Series
CDS img
Defence
UPSC CDS 2026 Mock Test Series
536 Tests 4 Tests Free
1767 Attempts
4.3(176)
English, Hindi
More Questions from CDS

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App