Precalculus Examples

$\cos (\frac{x}{2}) + \cos (\frac{3 x}{2})$

Step 1

Simplify each term.

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Step 1.1

Apply the cosine half-angle identity $\cos (\frac{x}{2}) = \pm \sqrt{\frac{1 + \cos (x)}{2}}$ .

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

Step 1.2

Rewrite $\sqrt{\frac{1 + \cos (x)}{2}}$ as $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ .

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

Step 1.3

Multiply $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

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

Step 1.4

Combine and simplify the denominator.

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Step 1.4.1

Multiply $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

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

Step 1.4.2

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

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

Step 1.4.3

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

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

Step 1.4.4

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

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

Step 1.4.5

Add $1$ and $1$ .

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

Step 1.4.6

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

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Step 1.4.6.1

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

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

Step 1.4.6.2

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

$\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{1}{2} \cdot 2}} + \cos (\frac{3 x}{2})$

Step 1.4.6.3

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

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

Step 1.4.6.4

Cancel the common factor of $2$ .

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Step 1.4.6.4.1

Cancel the common factor.

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

Step 1.4.6.4.2

Rewrite the expression.

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

Step 1.4.6.5

Evaluate the exponent.

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

Step 1.5

Combine using the product rule for radicals.

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

Step 1.6

Factor $3$ out of $\frac{3 x}{2}$ .

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

Step 1.7

Use the triple-angle identity to transform $\cos (3 x)$ to $4 \cos^{3} (x) - 3 \cos (x)$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 \cos^{3} (\frac{x}{2}) - 3 \cos (\frac{x}{2})$

Step 1.8

Simplify each term.

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Step 1.8.1

Apply the cosine half-angle identity $\cos (\frac{x}{2}) = \pm \sqrt{\frac{1 + \cos (x)}{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \sqrt{\frac{1 + \cos (x)}{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.2

Rewrite $\sqrt{\frac{1 + \cos (x)}{2}}$ as $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)}}{\sqrt{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.3

Multiply $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)}}{\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4

Combine and simplify the denominator.

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Step 1.8.4.1

Multiply $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{\sqrt{2} \sqrt{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.2

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{1} \sqrt{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.3

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{1} {\sqrt{2}}^{1}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.4

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{1 + 1}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.5

Add $1$ and $1$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.6

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

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Step 1.8.4.6.1

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{(2^{\frac{1}{2}})}^{2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.6.2

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{1}{2} \cdot 2}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.6.3

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{2}{2}}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.6.4

Cancel the common factor of $2$ .

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Step 1.8.4.6.4.1

Cancel the common factor.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{2}{2}}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.6.4.2

Rewrite the expression.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{1}})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.4.6.5

Evaluate the exponent.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.5

Combine using the product rule for radicals.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 \cos (\frac{x}{2})$

Step 1.8.6

Apply the cosine half-angle identity $\cos (\frac{x}{2}) = \pm \sqrt{\frac{1 + \cos (x)}{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \sqrt{\frac{1 + \cos (x)}{2}})$

Step 1.8.7

Rewrite $\sqrt{\frac{1 + \cos (x)}{2}}$ as $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)}}{\sqrt{2}})$

Step 1.8.8

Multiply $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)}}{\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}})$

Step 1.8.9

Combine and simplify the denominator.

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Step 1.8.9.1

Multiply $\frac{\sqrt{1 + \cos (x)}}{\sqrt{2}}$ by $\frac{\sqrt{2}}{\sqrt{2}}$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{\sqrt{2} \sqrt{2}})$

Step 1.8.9.2

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{1} \sqrt{2}})$

Step 1.8.9.3

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{1} {\sqrt{2}}^{1}})$

Step 1.8.9.4

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{1 + 1}})$

Step 1.8.9.5

Add $1$ and $1$ .

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{\sqrt{2}}^{2}})$

Step 1.8.9.6

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

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Step 1.8.9.6.1

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{{(2^{\frac{1}{2}})}^{2}})$

Step 1.8.9.6.2

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{1}{2} \cdot 2}})$

Step 1.8.9.6.3

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

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{2}{2}}})$

Step 1.8.9.6.4

Cancel the common factor of $2$ .

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Step 1.8.9.6.4.1

Cancel the common factor.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{\frac{2}{2}}})$

Step 1.8.9.6.4.2

Rewrite the expression.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2^{1}})$

Step 1.8.9.6.5

Evaluate the exponent.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{1 + \cos (x)} \sqrt{2}}{2})$

Step 1.8.10

Combine using the product rule for radicals.

$\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2} + 4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 3 (\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})$

Step 2

Simplify by adding terms.

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Step 2.1

Subtract $3 (\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})$ from $\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2}$ .

$4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 2 (\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})$

Step 2.2

Reorder factors in $4 {(\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})}^{3} - 2 (\pm \frac{\sqrt{(1 + \cos (x)) \cdot 2}}{2})$ .

$4 {(\pm \frac{\sqrt{2 (1 + \cos (x))}}{2})}^{3} - 2 (\pm \frac{\sqrt{2 (1 + \cos (x))}}{2})$