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Question

The value of \(\frac{{\rm cose{c^2}30^\circ {{\rm \sin }^2}45^\circ + {{\rm \sec }^2}60^\circ }}{{\rm tan60^\circ \rm cose{c^2}45^\circ - {{\rm \sec }^2}60^\circ \rm tan45^\circ }}\)  is:

This question was previously asked in
SSC CGL 2019 (Tier 2) GS Finance & Economics Previous Year Paper (17-Nov-2020)
The correct answer is

3/(√3 - 2)

Evaluating the Trigonometric Expression Value

This solution explains how to find the value of the given trigonometric expression involving specific angles.

Key Trigonometric Values Needed

To solve this problem, we first need to recall the values of the trigonometric functions for the angles 30°, 45°, and 60°.

Trigonometric Function Angle (\(^\circ\)) Value Squared Value (\( ^2 \))
\(\rm cosec\) 30 2 4
\(\rm \sin\) 45 \(\frac{1}{\sqrt{2}}\) \(\frac{1}{2}\)
\(\rm \sec\) 60 2 4
\(\rm tan\) 60 \(\sqrt{3}\) 3
\(\rm cosec\) 45 \(\sqrt{2}\) 2
\(\rm tan\) 45 1 1

Step-by-Step Calculation of the Expression

The expression given is:

\(\frac{{\rm cose{c^2}30^\circ {{\rm \sin }^2}45^\circ + {{\rm \sec }^2}60^\circ }}{{\rm tan60^\circ \rm cose{c^2}45^\circ - {{\rm \sec }^2}60^\circ \rm tan45^\circ }}\)

Numerator Calculation

Let's calculate the value of the numerator first:

\(\rm cose{c^2}30^\circ {{\rm \sin }^2}45^\circ + {{\rm \sec }^2}60^\circ\)

Substitute the known values:

\( = (2)^2 \times \left(\frac{1}{\sqrt{2}}\right)^2 + (2)^2 \)

Simplify the squares:

\( = 4 \times \frac{1}{2} + 4 \)

Perform the multiplication:

\( = 2 + 4 \)

Result of the numerator:

\( = 6 \)

Denominator Calculation

Now, let's calculate the value of the denominator:

\(\rm tan60^\circ \rm cose{c^2}45^\circ - {{\rm \sec }^2}60^\circ \rm tan45^\circ\)

Substitute the known values:

\( = (\sqrt{3}) \times (\sqrt{2})^2 - (2)^2 \times (1) \)

Simplify the squares and multiplication:

\( = \sqrt{3} \times 2 - 4 \times 1 \)

\( = 2\sqrt{3} - 4 \)

Calculating the Final Expression Value

Now, divide the calculated numerator by the calculated denominator:

\(\text{Expression Value} = \frac{\text{Numerator}}{\text{Denominator}} = \frac{6}{2\sqrt{3} - 4}\)

We can simplify this fraction by factoring out a 2 from the denominator:

\( = \frac{6}{2(\sqrt{3} - 2)} \)

Cancel out the common factor of 2:

\( = \frac{3}{\sqrt{3} - 2} \)

Comparing the Result with Options

The calculated value of the expression is \(\frac{3}{\sqrt{3} - 2}\).

Comparing this result with the given options:

  • Option 1: \(\frac{-3}{2 + \sqrt{3}}\)
  • Option 2: \(\frac{3}{\sqrt{3} - 2}\)
  • Option 3: \(\frac{3}{2 + \sqrt{3}}\)
  • Option 4: \(\frac{-3}{\sqrt{3} - 2}\)

Our calculated value \(\frac{3}{\sqrt{3} - 2}\) directly matches Option 2.

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