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Prove the following identity:

[tex]\[
\tan \frac{x}{2} + \cot \frac{x}{2} = 2 \csc x
\][/tex]

We begin by writing the left side using Reciprocal Identity to simplify:

[tex]\[
\tan \frac{x}{2} + \cot \frac{x}{2} = \tan \frac{x}{2} + \frac{1}{\tan \frac{x}{2}}
\][/tex]


Sagot :

Certainly! Let's prove the given trigonometric identity step by step:

[tex]\[ \tan \frac{x}{2} + \cot \frac{x}{2} = 2 \csc x \][/tex]

1. Express [tex]\(\tan\frac{x}{2}\)[/tex] and [tex]\(\cot\frac{x}{2}\)[/tex] using sine and cosine:

[tex]\[ \tan\frac{x}{2} = \frac{\sin\frac{x}{2}}{\cos\frac{x}{2}} \][/tex]
[tex]\[ \cot\frac{x}{2} = \frac{\cos\frac{x}{2}}{\sin\frac{x}{2}} \][/tex]

2. Combine [tex]\(\tan\frac{x}{2}\)[/tex] and [tex]\(\cot\frac{x}{2}\)[/tex] over a common denominator:

[tex]\[ \tan\frac{x}{2} + \cot\frac{x}{2} = \frac{\sin\frac{x}{2}}{\cos\frac{x}{2}} + \frac{\cos\frac{x}{2}}{\sin\frac{x}{2}} \][/tex]

[tex]\[ = \frac{\sin^2\frac{x}{2} + \cos^2\frac{x}{2}}{\sin\frac{x}{2} \cos\frac{x}{2}} \][/tex]

3. Use the Pythagorean identity:

[tex]\[ \sin^2\frac{x}{2} + \cos^2\frac{x}{2} = 1 \][/tex]

Therefore:

[tex]\[ \tan\frac{x}{2} + \cot\frac{x}{2} = \frac{1}{\sin\frac{x}{2} \cos\frac{x}{2}} \][/tex]

4. Recall the double-angle identity for sine:

[tex]\[ \sin x = 2 \sin\frac{x}{2} \cos\frac{x}{2} \][/tex]

This means:

[tex]\[ \sin\frac{x}{2} \cos\frac{x}{2} = \frac{\sin x}{2} \][/tex]

5. Substitute this back into the expression:

[tex]\[ \tan\frac{x}{2} + \cot\frac{x}{2} = \frac{1}{\frac{\sin x}{2}} = \frac{2}{\sin x} \][/tex]

6. Use the definition of cosecant:

[tex]\[ \csc x = \frac{1}{\sin x} \][/tex]

So:

[tex]\[ \frac{2}{\sin x} = 2 \csc x \][/tex]

Therefore:

[tex]\[ \tan\frac{x}{2} + \cot\frac{x}{2} = 2 \csc x \][/tex]

This completes our proof! The identity [tex]\(\tan\frac{x}{2} + \cot\frac{x}{2} = 2 \csc x\)[/tex] has been successfully proven.