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The expression [tex]$\frac{1+\tan x}{-1+\tan x}$[/tex] can be rewritten as which of the following?

A. [tex]$\tan \left(\frac{3 \pi}{4}-x\right)$[/tex]

B. [tex][tex]$\tan \left(\frac{3 \pi}{4}+x\right)$[/tex][/tex]

C. [tex]$\tan \left(\frac{\pi}{4}-x\right)$[/tex]

D. [tex]$\tan \left(\frac{\pi}{4}+x\right)$[/tex]

Sagot :

To determine which expression is equivalent to [tex]\(\frac{1+\tan x}{-1+\tan x}\)[/tex], we need to recognize the trigonometric identities that simplify this expression. Let's systematically check each option to see which one matches our expression.

### Step-by-Step Solution:

1. Given Expression:

[tex]\[ \frac{1+\tan x}{-1+\tan x} \][/tex]

2. Option 1: [tex]\(\tan \left(\frac{3 \pi}{4} - x\right)\)[/tex]

We start by using the identity for the tangent of a difference of two angles:

[tex]\[ \tan \left(\frac{3 \pi}{4} - x\right) = \frac{\tan \left(\frac{3 \pi}{4}\right) - \tan x}{1 + \tan \left(\frac{3 \pi}{4}\right) \tan x} \][/tex]

Since [tex]\(\tan \left(\frac{3 \pi}{4}\right) = -1\)[/tex]:

[tex]\[ \tan \left(\frac{3 \pi}{4} - x\right) = \frac{-1 - \tan x}{1 + (-1) \cdot \tan x} = \frac{-1 - \tan x}{1 - \tan x} \][/tex]

To match the given expression, let's multiply both the numerator and denominator by [tex]\(-1\)[/tex]:

[tex]\[ \frac{-1 - \tan x}{1 - \tan x} = \frac{-(1 + \tan x)}{-(1 - \tan x)} = \frac{1 + \tan x}{-1 + \tan x} \][/tex]

This simplifies directly to the given expression. So, this option is correct.

3. Option 2: [tex]\(\tan \left(\frac{3 \pi}{4} + x\right)\)[/tex]

Using the addition formula for tangent:

[tex]\[ \tan \left(\frac{3 \pi}{4} + x\right) = \frac{\tan \left(\frac{3 \pi}{4}\right) + \tan x}{1 - \tan \left(\frac{3 \pi}{4}\right) \tan x} \][/tex]

Since [tex]\(\tan \left(\frac{3 \pi}{4}\right) = -1\)[/tex]:

[tex]\[ \tan \left(\frac{3 \pi}{4} + x\right) = \frac{-1 + \tan x}{1 - (-1) \cdot \tan x} = \frac{-1 + \tan x}{1 + \tan x} \][/tex]

This expression does not match the given expression. So, this option is incorrect.

4. Option 3: [tex]\(\tan \left(\frac{\pi}{4} - x\right)\)[/tex]

Using the identity for the tangent of a difference:

[tex]\[ \tan \left(\frac{\pi}{4} - x\right) = \frac{\tan \left(\frac{\pi}{4}\right) - \tan x}{1 + \tan \left(\frac{\pi}{4}\right) \tan x} \][/tex]

Since [tex]\(\tan \left(\frac{\pi}{4}\right) = 1\)[/tex]:

[tex]\[ \tan \left(\frac{\pi}{4} - x\right) = \frac{1 - \tan x}{1 + \tan x} \][/tex]

This does not match the given expression. So, this option is incorrect.

5. Option 4: [tex]\(\tan \left(\frac{\pi}{4} + x\right)\)[/tex]

Using the addition identity for tangent:

[tex]\[ \tan \left(\frac{\pi}{4} + x\right) = \frac{\tan \left(\frac{\pi}{4}\right) + \tan x}{1 - \tan \left(\frac{\pi}{4}\right) \tan x} \][/tex]

Since [tex]\(\tan \left(\frac{\pi}{4}\right) = 1\)[/tex]:

[tex]\[ \tan \left(\frac{\pi}{4} + x\right) = \frac{1 + \tan x}{1 - \tan x} \][/tex]

This expression does not match the given expression. So, this option is incorrect.

### Conclusion:

The given expression:

[tex]\[ \frac{1+\tan x}{-1+\tan x} \][/tex]

is equivalent to:

[tex]\[ \tan \left(\frac{3 \pi}{4} - x\right) \][/tex]

Thus, the correct option is:

[tex]\[ \tan \left(\frac{3 \pi}{4}-x\right) \][/tex]
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