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Question

If $\tan A = \frac{3}{4}$, then the value of $\frac{\cos A - \sin A}{\cos A + \sin A}$ is:

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
$\frac{1}{7}$

Problem Analysis:

  • We are given the value of $\tan A = \frac{3}{4}$.
  • We need to find the value of the expression $\frac{\cos A - \sin A}{\cos A + \sin A}$.

Trigonometric Expression Calculation

A straightforward method is to divide both the numerator and the denominator of the expression by $\cos A$. This allows us to use the given value of $\tan A$, since $\tan A = \frac{\sin A}{\cos A}$.

Expression: $ \frac{\cos A - \sin A}{\cos A + \sin A} $

Divide numerator and denominator by $\cos A$:

$ \frac{\frac{\cos A}{\cos A} - \frac{\sin A}{\cos A}}{\frac{\cos A}{\cos A} + \frac{\sin A}{\cos A}} $

Simplify using $\frac{\sin A}{\cos A} = \tan A$:

$ \frac{1 - \tan A}{1 + \tan A} $

Substituting the Value of tan A

Now, substitute the given value $\tan A = \frac{3}{4}$ into the simplified expression:

$ \frac{1 - \frac{3}{4}}{1 + \frac{3}{4}} $

Calculate the numerator and the denominator:

  • Numerator: $1 - \frac{3}{4} = \frac{4}{4} - \frac{3}{4} = \frac{1}{4}$
  • Denominator: $1 + \frac{3}{4} = \frac{4}{4} + \frac{3}{4} = \frac{7}{4}$

Now, perform the division:

$ \frac{\frac{1}{4}}{\frac{7}{4}} $

To divide fractions, multiply by the reciprocal of the denominator:

$ \frac{1}{4} \times \frac{4}{7} = \frac{1}{7} $

Thus, the value of the expression is $\frac{1}{7}$.

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