What is the exact value of [tex]\tan \left(67.5^{\circ}\right)[/tex]?

A. [tex]\sqrt{3}[/tex]
B. [tex]\frac{\sqrt{3}}{3}[/tex]
C. [tex]\sqrt{\frac{2-\sqrt{2}}{2+\sqrt{2}}}[/tex]
D. [tex]\sqrt{\frac{2+\sqrt{2}}{2-\sqrt{2}}}[/tex]



Answer :

To find the exact value of [tex]\(\tan \left(67.5^{\circ}\right)\)[/tex], let's break it down step by step using trigonometric identities and known values.

First, recognize that [tex]\(67.5^{\circ} = 45^{\circ} + 22.5^{\circ}\)[/tex]. We can use the tangent addition formula:
[tex]\[ \tan(A + B) = \frac{\tan(A) + \tan(B)}{1 - \tan(A) \tan(B)} \][/tex]
Here, [tex]\(A = 45^{\circ}\)[/tex] and [tex]\(B = 22.5^{\circ}\)[/tex].

1. Calculate [tex]\(\tan(45^{\circ})\)[/tex]:
[tex]\[ \tan(45^{\circ}) = 1 \][/tex]

2. Calculate [tex]\(\tan(22.5^{\circ})\)[/tex]:

We use the relationship:
[tex]\[ \tan(22.5^{\circ}) = \sqrt{\frac{1 - \sin(45^{\circ})}{1 + \sin(45^{\circ})}} \][/tex]

Knowing that [tex]\(\sin(45^{\circ}) = \frac{\sqrt{2}}{2}\)[/tex]:
[tex]\[ \tan(22.5^{\circ}) = \sqrt{\frac{1 - \frac{\sqrt{2}}{2}}{1 + \frac{\sqrt{2}}{2}}} \][/tex]

Simplify the fraction:
[tex]\[ \tan(22.5^{\circ}) = \sqrt{\frac{2 - \sqrt{2}}{2 + \sqrt{2}}} \][/tex]

3. Use the tangent addition formula:

Now we apply the formula:
[tex]\[ \tan(67.5^{\circ}) = \frac{\tan(45^{\circ}) + \tan(22.5^{\circ})}{1 - \tan(45^{\circ}) \tan(22.5^{\circ})} \][/tex]

Substituting the values:
[tex]\[ \tan(67.5^{\circ}) = \frac{1 + \sqrt{\frac{2 - \sqrt{2}}{2 + \sqrt{2}}}}{1 - 1 \cdot \sqrt{\frac{2 - \sqrt{2}}{2 + \sqrt{2}}}} \][/tex]

Given the simplifications and the known results:
[tex]\[ \tan(67.5^{\circ}) = 2.414213562373096 \][/tex]

Given the options, the correct answer can be identified as:
[tex]\[ \tan(22.5^{\circ}) = \sqrt{\frac{2 - \sqrt{2}}{2 + \sqrt{2}}} \][/tex]

Therefore, the exact value we are looking for:
[tex]\[ \sqrt{\frac{2 + \sqrt{2}}{2 - \sqrt{2}}} \][/tex]

[tex]\[ \boxed{\sqrt{\frac{2+\sqrt{2}}{2-\sqrt{2}}}} \][/tex]