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Question

If $\tan\theta + \cot\theta = 6$, then find the value of $\tan^2\theta + \cot^2\theta$

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
34

Solving Trigonometric Expression: Tan^2 Theta + Cot^2 Theta

We are given the equation:

$ \tan\theta + \cot\theta = 6 $

We need to find the value of the expression:

$ \tan^2\theta + \cot^2\theta $

Applying Algebraic Identity

Let's square both sides of the given equation:

$ (\tan\theta + \cot\theta)^2 = 6^2 $

Using the algebraic identity $ (a+b)^2 = a^2 + b^2 + 2ab $, we expand the left side:

$ \tan^2\theta + \cot^2\theta + 2(\tan\theta)(\cot\theta) = 36 $

Simplifying the Trigonometric Term

We know that $ \cot\theta = \frac{1}{\tan\theta} $. Therefore, the product $ (\tan\theta)(\cot\theta) $ simplifies to 1:

$ \tan\theta \cdot \cot\theta = \tan\theta \cdot \frac{1}{\tan\theta} = 1 $

Substituting this back into the expanded equation:

$ \tan^2\theta + \cot^2\theta + 2(1) = 36 $

$ \tan^2\theta + \cot^2\theta + 2 = 36 $

Calculating the Final Value

To find the required value, isolate $ \tan^2\theta + \cot^2\theta $ by subtracting 2 from both sides:

$ \tan^2\theta + \cot^2\theta = 36 - 2 $

$ \tan^2\theta + \cot^2\theta = 34 $

Thus, the value of $ \tan^2\theta + \cot^2\theta $ is 34.

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