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Question

If A = π / 6 and B = π / 3, then consider the following statements:

I. sin A + sin B = cos A + cos B

II. tan A + tan B = cot A + cot B

Which of the above statements is / are correct?

The correct answer is

Both I and II

Verifying Trigonometric Statements for Specific Angles

The problem asks us to verify the correctness of two trigonometric statements given specific values for angles A and B. The given values are $\text{A} = \frac{\pi}{6}$ and $\text{B} = \frac{\pi}{3}$.

First, let's convert the angles from radians to degrees for easier understanding of common trigonometric values:

  • $\text{A} = \frac{\pi}{6} \text{ radians} = \frac{180^\circ}{6} = 30^\circ$
  • $\text{B} = \frac{\pi}{3} \text{ radians} = \frac{180^\circ}{3} = 60^\circ$

Calculating Trigonometric Ratios for A and B

Now, let's find the values of the trigonometric ratios for A = $30^\circ$ and B = $60^\circ$:

  • For $\text{A} = 30^\circ$:
    • $\text{sin A} = \text{sin } 30^\circ = \frac{1}{2}$
    • $\text{cos A} = \text{cos } 30^\circ = \frac{\sqrt{3}}{2}$
    • $\text{tan A} = \text{tan } 30^\circ = \frac{1}{\sqrt{3}}$
    • $\text{cot A} = \text{cot } 30^\circ = \sqrt{3}$
  • For $\text{B} = 60^\circ$:
    • $\text{sin B} = \text{sin } 60^\circ = \frac{\sqrt{3}}{2}$
    • $\text{cos B} = \text{cos } 60^\circ = \frac{1}{2}$
    • $\text{tan B} = \text{tan } 60^\circ = \sqrt{3}$
    • $\text{cot B} = \text{cot } 60^\circ = \frac{1}{\sqrt{3}}$

Evaluating Statement I: sin A + sin B = cos A + cos B

Let's substitute the calculated values into Statement I:

Left Hand Side (LHS): $\text{sin A} + \text{sin B} = \text{sin } 30^\circ + \text{sin } 60^\circ = \frac{1}{2} + \frac{\sqrt{3}}{2} = \frac{1 + \sqrt{3}}{2}$

Right Hand Side (RHS): $\text{cos A} + \text{cos B} = \text{cos } 30^\circ + \text{cos } 60^\circ = \frac{\sqrt{3}}{2} + \frac{1}{2} = \frac{\sqrt{3} + 1}{2}$

Comparing LHS and RHS:

$\frac{1 + \sqrt{3}}{2} = \frac{\sqrt{3} + 1}{2}$

The LHS is equal to the RHS. Therefore, Statement I is correct for the given values of A and B.

Evaluating Statement II: tan A + tan B = cot A + cot B

Now, let's substitute the calculated values into Statement II:

Left Hand Side (LHS): $\text{tan A} + \text{tan B} = \text{tan } 30^\circ + \text{tan } 60^\circ = \frac{1}{\sqrt{3}} + \sqrt{3}$

To add these, find a common denominator:

$\frac{1}{\sqrt{3}} + \sqrt{3} = \frac{1}{\sqrt{3}} + \frac{\sqrt{3} \times \sqrt{3}}{\sqrt{3}} = \frac{1}{\sqrt{3}} + \frac{3}{\sqrt{3}} = \frac{1 + 3}{\sqrt{3}} = \frac{4}{\sqrt{3}}$

Right Hand Side (RHS): $\text{cot A} + \text{cot B} = \text{cot } 30^\circ + \text{cot } 60^\circ = \sqrt{3} + \frac{1}{\sqrt{3}}$

Similarly, find a common denominator:

$\sqrt{3} + \frac{1}{\sqrt{3}} = \frac{\sqrt{3} \times \sqrt{3}}{\sqrt{3}} + \frac{1}{\sqrt{3}} = \frac{3}{\sqrt{3}} + \frac{1}{\sqrt{3}} = \frac{3 + 1}{\sqrt{3}} = \frac{4}{\sqrt{3}}$

Comparing LHS and RHS:

$\frac{4}{\sqrt{3}} = \frac{4}{\sqrt{3}}$

The LHS is equal to the RHS. Therefore, Statement II is correct for the given values of A and B.

Conclusion

Based on the evaluation of both statements using the given values $\text{A} = \frac{\pi}{6}$ and $\text{B} = \frac{\pi}{3}$, we found that both Statement I and Statement II are correct.

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Important Questions from Trigonometric Ratios

  1. If \(cosec~\theta =\frac{29}{21}\) where 0 < θ < 90°, then what is the value of 4 sec θ + 4 tan θ?

  2. The value of \(\cot \left( {cose{c^{ - 1}}\frac{5}{3} + {{\tan }^{ - 1}}\frac{2}{3}\;} \right)\)

  3. The distance of the highest point on the graph of the function y = √3 cos x + sin x from the x-axis is:

  4. If \(\sin A = \frac{1}{{\sqrt 2 }}\) and \({\mathop{\rm Cos}\nolimits} B = \frac{{\sqrt 3 }}{2}\), then, find the value of (A + B)º.

    A. 60º 

    B. 75º 

    C. 105º 

    D. 90º 

  5. \(\frac{\sin \theta-\cos \theta+1}{\sin \theta+\cos \theta-1}\) is equal to
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