Find the Exact Value cos((11pi)/12)cos(pi/6)+sin((11pi)/12)sin(pi/6)

$\cos (\frac{11 π}{12}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Step 1

Simplify each term.

The exact value of $\cos (\frac{11 π}{12})$ is $- \frac{\sqrt{6} + \sqrt{2}}{4}$ .

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.

$- \cos (\frac{π}{12}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Split $\frac{π}{12}$ into two angles where the values of the six trigonometric functions are known.

$- \cos (\frac{π}{4} - \frac{π}{6}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Apply the difference of angles identity $\cos (x - y) = \cos (x) \cos (y) + \sin (x) \sin (y)$ .

$- (\cos (\frac{π}{4}) \cos (\frac{π}{6}) + \sin (\frac{π}{4}) \sin (\frac{π}{6})) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

The exact value of $\cos (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$- (\frac{\sqrt{2}}{2} \cos (\frac{π}{6}) + \sin (\frac{π}{4}) \sin (\frac{π}{6})) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

The exact value of $\cos (\frac{π}{6})$ is $\frac{\sqrt{3}}{2}$ .

$- (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} + \sin (\frac{π}{4}) \sin (\frac{π}{6})) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

The exact value of $\sin (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$- (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} + \frac{\sqrt{2}}{2} \sin (\frac{π}{6})) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

The exact value of $\sin (\frac{π}{6})$ is $\frac{1}{2}$ .

$- (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} + \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

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

Simplify each term.

Multiply $\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2}$ .

Multiply $\frac{\sqrt{2}}{2}$ by $\frac{\sqrt{3}}{2}$ .

$- (\frac{\sqrt{2} \sqrt{3}}{2 \cdot 2} + \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Combine using the product rule for radicals.

$- (\frac{\sqrt{2 \cdot 3}}{2 \cdot 2} + \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $2$ by $3$ .

$- (\frac{\sqrt{6}}{2 \cdot 2} + \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $2$ by $2$ .

$- (\frac{\sqrt{6}}{4} + \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $\frac{\sqrt{2}}{2} \cdot \frac{1}{2}$ .

Multiply $\frac{\sqrt{2}}{2}$ by $\frac{1}{2}$ .

$- (\frac{\sqrt{6}}{4} + \frac{\sqrt{2}}{2 \cdot 2}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $2$ by $2$ .

$- (\frac{\sqrt{6}}{4} + \frac{\sqrt{2}}{4}) \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Combine the numerators over the common denominator.

$- \frac{\sqrt{6} + \sqrt{2}}{4} \cos (\frac{π}{6}) + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

The exact value of $\cos (\frac{π}{6})$ is $\frac{\sqrt{3}}{2}$ .

$- \frac{\sqrt{6} + \sqrt{2}}{4} \cdot \frac{\sqrt{3}}{2} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $- \frac{\sqrt{6} + \sqrt{2}}{4} \cdot \frac{\sqrt{3}}{2}$ .

Multiply $\frac{\sqrt{3}}{2}$ by $\frac{\sqrt{6} + \sqrt{2}}{4}$ .

$- \frac{\sqrt{3} (\sqrt{6} + \sqrt{2})}{2 \cdot 4} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $2$ by $4$ .

$- \frac{\sqrt{3} (\sqrt{6} + \sqrt{2})}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Apply the distributive property.

$- \frac{\sqrt{3} \sqrt{6} + \sqrt{3} \sqrt{2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Combine using the product rule for radicals.

$- \frac{\sqrt{3 \cdot 6} + \sqrt{3} \sqrt{2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Combine using the product rule for radicals.

$- \frac{\sqrt{3 \cdot 6} + \sqrt{3 \cdot 2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Simplify each term.

Multiply $3$ by $6$ .

$- \frac{\sqrt{18} + \sqrt{3 \cdot 2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Rewrite $18$ as $3^{2} \cdot 2$ .

Factor $9$ out of $18$ .

$- \frac{\sqrt{9 (2)} + \sqrt{3 \cdot 2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

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

$- \frac{\sqrt{3^{2} \cdot 2} + \sqrt{3 \cdot 2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Pull terms out from under the radical.

$- \frac{3 \sqrt{2} + \sqrt{3 \cdot 2}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

Multiply $3$ by $2$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \sin (\frac{11 π}{12}) \sin (\frac{π}{6})$

The exact value of $\sin (\frac{11 π}{12})$ is $\frac{\sqrt{6} - \sqrt{2}}{4}$ .

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \sin (\frac{π}{12}) \sin (\frac{π}{6})$

Split $\frac{π}{12}$ into two angles where the values of the six trigonometric functions are known.

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \sin (\frac{π}{4} - \frac{π}{6}) \sin (\frac{π}{6})$

Apply the difference of angles identity.

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\sin (\frac{π}{4}) \cos (\frac{π}{6}) - \cos (\frac{π}{4}) \sin (\frac{π}{6})) \sin (\frac{π}{6})$

The exact value of $\sin (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{2}}{2} \cos (\frac{π}{6}) - \cos (\frac{π}{4}) \sin (\frac{π}{6})) \sin (\frac{π}{6})$

The exact value of $\cos (\frac{π}{6})$ is $\frac{\sqrt{3}}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \cos (\frac{π}{4}) \sin (\frac{π}{6})) \sin (\frac{π}{6})$

The exact value of $\cos (\frac{π}{4})$ is $\frac{\sqrt{2}}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \sin (\frac{π}{6})) \sin (\frac{π}{6})$

The exact value of $\sin (\frac{π}{6})$ is $\frac{1}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \sin (\frac{π}{6})$

Simplify $\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}$ .

Simplify each term.

Multiply $\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2}$ .

Multiply $\frac{\sqrt{2}}{2}$ by $\frac{\sqrt{3}}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{2} \sqrt{3}}{2 \cdot 2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \sin (\frac{π}{6})$

Combine using the product rule for radicals.

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{2 \cdot 3}}{2 \cdot 2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \sin (\frac{π}{6})$

Multiply $2$ by $3$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{6}}{2 \cdot 2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \sin (\frac{π}{6})$

Multiply $2$ by $2$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \sin (\frac{π}{6})$

Multiply $- \frac{\sqrt{2}}{2} \cdot \frac{1}{2}$ .

Multiply $\frac{1}{2}$ by $\frac{\sqrt{2}}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{2 \cdot 2}) \sin (\frac{π}{6})$

Multiply $2$ by $2$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + (\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{4}) \sin (\frac{π}{6})$

Combine the numerators over the common denominator.

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \frac{\sqrt{6} - \sqrt{2}}{4} \sin (\frac{π}{6})$

The exact value of $\sin (\frac{π}{6})$ is $\frac{1}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \frac{\sqrt{6} - \sqrt{2}}{4} \cdot \frac{1}{2}$

Multiply $\frac{\sqrt{6} - \sqrt{2}}{4} \cdot \frac{1}{2}$ .

Multiply $\frac{\sqrt{6} - \sqrt{2}}{4}$ by $\frac{1}{2}$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \frac{\sqrt{6} - \sqrt{2}}{4 \cdot 2}$

Multiply $4$ by $2$ .

$- \frac{3 \sqrt{2} + \sqrt{6}}{8} + \frac{\sqrt{6} - \sqrt{2}}{8}$

Step 2

Combine the numerators over the common denominator.

$\frac{- (3 \sqrt{2} + \sqrt{6}) + \sqrt{6} - \sqrt{2}}{8}$

Step 3

Simplify each term.

Apply the distributive property.

$\frac{- (3 \sqrt{2}) - \sqrt{6} + \sqrt{6} - \sqrt{2}}{8}$

Multiply $3$ by $- 1$ .

$\frac{- 3 \sqrt{2} - \sqrt{6} + \sqrt{6} - \sqrt{2}}{8}$

Step 4

Simplify terms.

Subtract $\sqrt{2}$ from $- 3 \sqrt{2}$ .

$\frac{- 4 \sqrt{2} - \sqrt{6} + \sqrt{6}}{8}$

Add $- \sqrt{6}$ and $\sqrt{6}$ .

$\frac{- 4 \sqrt{2} + 0}{8}$

Add $- 4 \sqrt{2}$ and $0$ .

$\frac{- 4 \sqrt{2}}{8}$

Cancel the common factor of $- 4$ and $8$ .

Factor $4$ out of $- 4 \sqrt{2}$ .

$\frac{4 (- \sqrt{2})}{8}$

Cancel the common factors.

Factor $4$ out of $8$ .

$\frac{4 (- \sqrt{2})}{4 (2)}$

Cancel the common factor.

$\frac{4 (- \sqrt{2})}{4 \cdot 2}$

Rewrite the expression.

$\frac{- \sqrt{2}}{2}$

Move the negative in front of the fraction.

$- \frac{\sqrt{2}}{2}$

Step 5

The result can be shown in multiple forms.

Exact Form:

$- \frac{\sqrt{2}}{2}$

Decimal Form:

$- 0.70710678 \dots$

Find the Exact Value cos((11pi)/12)cos(pi/6)+sin((11pi)/12)sin(pi/6)

Related Questions

Support LCMGCF.com by disabling your adblocker.