Precalculus Examples

$\sin (195) \cdot \cos (45)$

Step 1

The exact value of $\sin (195)$ is $- \frac{\sqrt{6} - \sqrt{2}}{4}$ .

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Step 1.1

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

$- \sin (15) \cdot \cos (45)$

Step 1.2

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

$- \sin (45 - 30) \cdot \cos (45)$

Step 1.3

Separate negation.

$- \sin (45 - (30)) \cdot \cos (45)$

Step 1.4

Apply the difference of angles identity.

$- (\sin (45) \cos (30) - \cos (45) \sin (30)) \cdot \cos (45)$

Step 1.5

The exact value of $\sin (45)$ is $\frac{\sqrt{2}}{2}$ .

$- (\frac{\sqrt{2}}{2} \cos (30) - \cos (45) \sin (30)) \cdot \cos (45)$

Step 1.6

The exact value of $\cos (30)$ is $\frac{\sqrt{3}}{2}$ .

$- (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \cos (45) \sin (30)) \cdot \cos (45)$

Step 1.7

The exact value of $\cos (45)$ is $\frac{\sqrt{2}}{2}$ .

$- (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \sin (30)) \cdot \cos (45)$

Step 1.8

The exact value of $\sin (30)$ is $\frac{1}{2}$ .

$- (\frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cdot \cos (45)$

Step 1.9

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

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Step 1.9.1

Simplify each term.

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Step 1.9.1.1

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

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Step 1.9.1.1.1

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

$- (\frac{\sqrt{2} \sqrt{3}}{2 \cdot 2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cdot \cos (45)$

Step 1.9.1.1.2

Combine using the product rule for radicals.

$- (\frac{\sqrt{2 \cdot 3}}{2 \cdot 2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cdot \cos (45)$

Step 1.9.1.1.3

Multiply $2$ by $3$ .

$- (\frac{\sqrt{6}}{2 \cdot 2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cdot \cos (45)$

Step 1.9.1.1.4

Multiply $2$ by $2$ .

$- (\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2}) \cdot \cos (45)$

Step 1.9.1.2

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

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Step 1.9.1.2.1

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

$- (\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{2 \cdot 2}) \cdot \cos (45)$

Step 1.9.1.2.2

Multiply $2$ by $2$ .

$- (\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{4}) \cdot \cos (45)$

Step 1.9.2

Combine the numerators over the common denominator.

$- \frac{\sqrt{6} - \sqrt{2}}{4} \cdot \cos (45)$

Step 2

The exact value of $\cos (45)$ is $\frac{\sqrt{2}}{2}$ .

$- \frac{\sqrt{6} - \sqrt{2}}{4} \cdot \frac{\sqrt{2}}{2}$

Step 3

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

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Step 3.1

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

$- \frac{\sqrt{2} (\sqrt{6} - \sqrt{2})}{2 \cdot 4}$

Step 3.2

Multiply $2$ by $4$ .

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

Step 4

Apply the distributive property.

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

Step 5

Combine using the product rule for radicals.

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

Step 6

Multiply $\sqrt{2} (- \sqrt{2})$ .

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Step 6.1

Raise $\sqrt{2}$ to the power of $1$ .

$- \frac{\sqrt{2 \cdot 6} - ({\sqrt{2}}^{1} \sqrt{2})}{8}$

Step 6.2

Raise $\sqrt{2}$ to the power of $1$ .

$- \frac{\sqrt{2 \cdot 6} - ({\sqrt{2}}^{1} {\sqrt{2}}^{1})}{8}$

Step 6.3

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

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

Step 6.4

Add $1$ and $1$ .

$- \frac{\sqrt{2 \cdot 6} - {\sqrt{2}}^{2}}{8}$

Step 7

Simplify each term.

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Step 7.1

Multiply $2$ by $6$ .

$- \frac{\sqrt{12} - {\sqrt{2}}^{2}}{8}$

Step 7.2

Rewrite $12$ as $2^{2} \cdot 3$ .

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Step 7.2.1

Factor $4$ out of $12$ .

$- \frac{\sqrt{4 (3)} - {\sqrt{2}}^{2}}{8}$

Step 7.2.2

Rewrite $4$ as $2^{2}$ .

$- \frac{\sqrt{2^{2} \cdot 3} - {\sqrt{2}}^{2}}{8}$

Step 7.3

Pull terms out from under the radical.

$- \frac{2 \sqrt{3} - {\sqrt{2}}^{2}}{8}$

Step 7.4

Rewrite ${\sqrt{2}}^{2}$ as $2$ .

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Step 7.4.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{2}$ as $2^{\frac{1}{2}}$ .

$- \frac{2 \sqrt{3} - {(2^{\frac{1}{2}})}^{2}}{8}$

Step 7.4.2

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$- \frac{2 \sqrt{3} - 2^{\frac{1}{2} \cdot 2}}{8}$

Step 7.4.3

Combine $\frac{1}{2}$ and $2$ .

$- \frac{2 \sqrt{3} - 2^{\frac{2}{2}}}{8}$

Step 7.4.4

Cancel the common factor of $2$ .

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Step 7.4.4.1

Cancel the common factor.

$- \frac{2 \sqrt{3} - 2^{\frac{2}{2}}}{8}$

Step 7.4.4.2

Rewrite the expression.

$- \frac{2 \sqrt{3} - 2^{1}}{8}$

Step 7.4.5

Evaluate the exponent.

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

Step 7.5

Multiply $- 1$ by $2$ .

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

Step 8

Cancel the common factor of $2 \sqrt{3} - 2$ and $8$ .

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Step 8.1

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

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

Step 8.2

Factor $2$ out of $- 2$ .

$- \frac{2 (\sqrt{3}) + 2 (- 1)}{8}$

Step 8.3

Factor $2$ out of $2 (\sqrt{3}) + 2 (- 1)$ .

$- \frac{2 (\sqrt{3} - 1)}{8}$

Step 8.4

Cancel the common factors.

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Step 8.4.1

Factor $2$ out of $8$ .

$- \frac{2 (\sqrt{3} - 1)}{2 (4)}$

Step 8.4.2

Cancel the common factor.

$- \frac{2 (\sqrt{3} - 1)}{2 \cdot 4}$

Step 8.4.3

Rewrite the expression.

$- \frac{\sqrt{3} - 1}{4}$

Step 9

The result can be shown in multiple forms.

Exact Form:

$- \frac{\sqrt{3} - 1}{4}$

Decimal Form:

$- 0.18301270 \dots$