Evaluate the given expression.
\[\frac{5}{1+\cot^2\theta} + \frac{3}{1+\tan^2\theta} + 2\cos^2\theta\]
5
Step 1: Simplify the Trigonometric Identities
Recall the following identities:
1. \(1 + \cot^2 \theta = \csc^2 \theta\)
2. \(1 + \tan^2 \theta = \sec^2 \theta\)
3. \(\csc \theta = \frac{1}{\sin \theta}\)
4. \(\sec \theta = \frac{1}{\cos \theta}\)
Substitute these into the expression:
\[\frac{5}{\csc^2 \theta} + \frac{3}{\sec^2 \theta} + 2 \cos^2 \theta\]
Step 2: Rewrite in Terms of Sine and Cosine
Since \(\csc \theta = \frac{1}{\sin \theta}\) and \(\sec \theta = \frac{1}{\cos \theta}\):
\[\frac{5}{\csc^2 \theta} = 5 \sin^2 \theta\]
\[\frac{3}{\sec^2 \theta} = 3 \cos^2 \theta\]
So the expression becomes:
\[5 \sin^2 \theta + 3 \cos^2 \theta + 2 \cos^2 \theta\]
Step 3: Combine Like Terms
Combine the \(\cos^2 \theta\) terms:
\[5 \sin^2 \theta + (3 \cos^2 \theta + 2 \cos^2 \theta) = 5 \sin^2 \theta + 5 \cos^2 \theta\]
Factor out the 5:
\[5 (\sin^2 \theta + \cos^2 \theta)\]
Step 4: Apply the Pythagorean Identity
We know that \(\sin^2 \theta + \cos^2 \theta = 1\), so:
\[5 (1) = 5\]
Final Answer:The expression simplifies to 5.
From the given options, the correct answer is 4. 5.
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