Find the Exact Value cot(15 degrees )

$\cot (15 °)$

Step 1

Split $15$ into two angles where the values of the six trigonometric functions are known.

$\cot (45 - 30)$

Step 2

Separate negation.

$\cot (45 - (30))$

Step 3

Apply the difference of angles identity.

$\frac{\cot (45) \cot (30) + 1}{\cot (30) - \cot (45)}$

Step 4

The exact value of $\cot (45)$ is $1$ .

$\frac{1 \cot (30) + 1}{\cot (30) - \cot (45)}$

Step 5

The exact value of $\cot (30)$ is $\sqrt{3}$ .

$\frac{1 \sqrt{3} + 1}{\cot (30) - \cot (45)}$

Step 6

The exact value of $\cot (30)$ is $\sqrt{3}$ .

$\frac{1 \sqrt{3} + 1}{\sqrt{3} - \cot (45)}$

Step 7

The exact value of $\cot (45)$ is $1$ .

$\frac{1 \sqrt{3} + 1}{\sqrt{3} - 1 \cdot 1}$

Step 8

Simplify $\frac{1 \sqrt{3} + 1}{\sqrt{3} - 1 \cdot 1}$ .

Multiply $\sqrt{3}$ by $1$ .

$\frac{\sqrt{3} + 1}{\sqrt{3} - 1 \cdot 1}$

Multiply $- 1$ by $1$ .

$\frac{\sqrt{3} + 1}{\sqrt{3} - 1}$

Multiply $\frac{\sqrt{3} + 1}{\sqrt{3} - 1}$ by $\frac{\sqrt{3} + 1}{\sqrt{3} + 1}$ .

$\frac{\sqrt{3} + 1}{\sqrt{3} - 1} \cdot \frac{\sqrt{3} + 1}{\sqrt{3} + 1}$

Multiply $\frac{\sqrt{3} + 1}{\sqrt{3} - 1}$ by $\frac{\sqrt{3} + 1}{\sqrt{3} + 1}$ .

$\frac{(\sqrt{3} + 1) (\sqrt{3} + 1)}{(\sqrt{3} - 1) (\sqrt{3} + 1)}$

Expand the denominator using the FOIL method.

$\frac{(\sqrt{3} + 1) (\sqrt{3} + 1)}{{\sqrt{3}}^{2} + \sqrt{3} - \sqrt{3} - 1}$

Simplify.

$\frac{(\sqrt{3} + 1) (\sqrt{3} + 1)}{2}$

Simplify the numerator.

Raise $\sqrt{3} + 1$ to the power of $1$ .

$\frac{{(\sqrt{3} + 1)}^{1} (\sqrt{3} + 1)}{2}$

Raise $\sqrt{3} + 1$ to the power of $1$ .

$\frac{{(\sqrt{3} + 1)}^{1} {(\sqrt{3} + 1)}^{1}}{2}$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$\frac{{(\sqrt{3} + 1)}^{1 + 1}}{2}$

Add $1$ and $1$ .

$\frac{{(\sqrt{3} + 1)}^{2}}{2}$

Simplify ${(\sqrt{3} + 1)}^{2}$ .

Rewrite ${(\sqrt{3} + 1)}^{2}$ as $(\sqrt{3} + 1) (\sqrt{3} + 1)$ .

$\frac{(\sqrt{3} + 1) (\sqrt{3} + 1)}{2}$

Expand $(\sqrt{3} + 1) (\sqrt{3} + 1)$ using the FOIL Method.

Apply the distributive property.

$\frac{\sqrt{3} (\sqrt{3} + 1) + 1 (\sqrt{3} + 1)}{2}$

Apply the distributive property.

$\frac{\sqrt{3} \sqrt{3} + \sqrt{3} \cdot 1 + 1 (\sqrt{3} + 1)}{2}$

Apply the distributive property.

$\frac{\sqrt{3} \sqrt{3} + \sqrt{3} \cdot 1 + 1 \sqrt{3} + 1 \cdot 1}{2}$

Simplify and combine like terms.

Simplify each term.

Combine using the product rule for radicals.

$\frac{\sqrt{3 \cdot 3} + \sqrt{3} \cdot 1 + 1 \sqrt{3} + 1 \cdot 1}{2}$

Multiply $3$ by $3$ .

$\frac{\sqrt{9} + \sqrt{3} \cdot 1 + 1 \sqrt{3} + 1 \cdot 1}{2}$

Rewrite $9$ as $3^{2}$ .

$\frac{\sqrt{3^{2}} + \sqrt{3} \cdot 1 + 1 \sqrt{3} + 1 \cdot 1}{2}$

Pull terms out from under the radical, assuming positive real numbers.

$\frac{3 + \sqrt{3} \cdot 1 + 1 \sqrt{3} + 1 \cdot 1}{2}$

Multiply $\sqrt{3}$ by $1$ .

$\frac{3 + \sqrt{3} + 1 \sqrt{3} + 1 \cdot 1}{2}$

Multiply $\sqrt{3}$ by $1$ .

$\frac{3 + \sqrt{3} + \sqrt{3} + 1 \cdot 1}{2}$

Multiply $1$ by $1$ .

$\frac{3 + \sqrt{3} + \sqrt{3} + 1}{2}$

Add $3$ and $1$ .

$\frac{4 + \sqrt{3} + \sqrt{3}}{2}$

Add $\sqrt{3}$ and $\sqrt{3}$ .

$\frac{4 + 2 \sqrt{3}}{2}$

Cancel the common factor of $4 + 2 \sqrt{3}$ and $2$ .

Factor $2$ out of $4$ .

$\frac{2 \cdot 2 + 2 \sqrt{3}}{2}$

Factor $2$ out of $2 \sqrt{3}$ .

$\frac{2 \cdot 2 + 2 (\sqrt{3})}{2}$

Factor $2$ out of $2 (2) + 2 (\sqrt{3})$ .

$\frac{2 (2 + \sqrt{3})}{2}$

Cancel the common factors.

Factor $2$ out of $2$ .

$\frac{2 (2 + \sqrt{3})}{2 (1)}$

Cancel the common factor.

$\frac{2 (2 + \sqrt{3})}{2 \cdot 1}$

Rewrite the expression.

$\frac{2 + \sqrt{3}}{1}$

Divide $2 + \sqrt{3}$ by $1$ .

$2 + \sqrt{3}$

Step 9

The result can be shown in multiple forms.

Exact Form:

$2 + \sqrt{3}$

Decimal Form:

$3.73205080 \dots$

Find the Exact Value cot(15 degrees )

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