Precalculus Examples

$\cos (2 x) = \frac{1}{\sqrt{2}}$

Step 1

Use the definition of cosine to find the known sides of the unit circle right triangle. The quadrant determines the sign on each of the values.

$\cos (2 x) = \frac{adjacent}{hypotenuse}$

Step 2

Find the opposite side of the unit circle triangle. Since the adjacent side and hypotenuse are known, use the Pythagorean theorem to find the remaining side.

$Opposite = \sqrt{{hypotenuse}^{2} - {adjacent}^{2}}$

Step 3

Replace the known values in the equation.

$Opposite = \sqrt{{(\sqrt{2})}^{2} - {(1)}^{2}}$

Step 4

Simplify inside the radical.

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Step 4.1

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

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Step 4.1.1

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

Opposite $= \sqrt{{(2^{\frac{1}{2}})}^{2} - {(1)}^{2}}$

Step 4.1.2

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

Opposite $= \sqrt{2^{\frac{1}{2} \cdot 2} - {(1)}^{2}}$

Step 4.1.3

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

Opposite $= \sqrt{2^{\frac{2}{2}} - {(1)}^{2}}$

Step 4.1.4

Cancel the common factor of $2$ .

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Step 4.1.4.1

Cancel the common factor.

Opposite $= \sqrt{2^{\frac{2}{2}} - {(1)}^{2}}$

Step 4.1.4.2

Rewrite the expression.

Opposite $= \sqrt{2 - {(1)}^{2}}$

Step 4.1.5

Evaluate the exponent.

Opposite $= \sqrt{2 - {(1)}^{2}}$

Step 4.2

One to any power is one.

Opposite $= \sqrt{2 - 1 \cdot 1}$

Step 4.3

Multiply $- 1$ by $1$ .

Opposite $= \sqrt{2 - 1}$

Step 4.4

Subtract $1$ from $2$ .

Opposite $= \sqrt{1}$

Step 4.5

Any root of $1$ is $1$ .

Opposite $= 1$

Step 5

Find the value of sine.

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Step 5.1

Use the definition of sine to find the value of $\sin (2 x)$ .

$\sin (2 x) = \frac{opp}{hyp}$

Step 5.2

Substitute in the known values.

$\sin (2 x) = \frac{1}{\sqrt{2}}$

Step 5.3

Simplify the value of $\sin (2 x)$ .

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Step 5.3.1

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

$\sin (2 x) = \frac{1}{\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}}$

Step 5.3.2

Combine and simplify the denominator.

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Step 5.3.2.1

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

$\sin (2 x) = \frac{\sqrt{2}}{\sqrt{2} \sqrt{2}}$

Step 5.3.2.2

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

$\sin (2 x) = \frac{\sqrt{2}}{\sqrt{2} \sqrt{2}}$

Step 5.3.2.3

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

$\sin (2 x) = \frac{\sqrt{2}}{\sqrt{2} \sqrt{2}}$

Step 5.3.2.4

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

$\sin (2 x) = \frac{\sqrt{2}}{{\sqrt{2}}^{1 + 1}}$

Step 5.3.2.5

Add $1$ and $1$ .

$\sin (2 x) = \frac{\sqrt{2}}{{\sqrt{2}}^{2}}$

Step 5.3.2.6

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

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Step 5.3.2.6.1

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

$\sin (2 x) = \frac{\sqrt{2}}{{(2^{\frac{1}{2}})}^{2}}$

Step 5.3.2.6.2

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

$\sin (2 x) = \frac{\sqrt{2}}{2^{\frac{1}{2} \cdot 2}}$

Step 5.3.2.6.3

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

$\sin (2 x) = \frac{\sqrt{2}}{2^{\frac{2}{2}}}$

Step 5.3.2.6.4

Cancel the common factor of $2$ .

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Step 5.3.2.6.4.1

Cancel the common factor.

$\sin (2 x) = \frac{\sqrt{2}}{2^{\frac{2}{2}}}$

Step 5.3.2.6.4.2

Rewrite the expression.

$\sin (2 x) = \frac{\sqrt{2}}{2}$

Step 5.3.2.6.5

Evaluate the exponent.

$\sin (2 x) = \frac{\sqrt{2}}{2}$

Step 6

Simplify the value of cosine.

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Step 6.1

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

$\cos (2 x) = \frac{1}{\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}}$

Step 6.2

Combine and simplify the denominator.

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Step 6.2.1

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

$\cos (2 x) = \frac{\sqrt{2}}{\sqrt{2} \sqrt{2}}$

Step 6.2.2

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

$\cos (2 x) = \frac{\sqrt{2}}{\sqrt{2} \sqrt{2}}$

Step 6.2.3

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

$\cos (2 x) = \frac{\sqrt{2}}{\sqrt{2} \sqrt{2}}$

Step 6.2.4

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

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

Step 6.2.5

Add $1$ and $1$ .

$\cos (2 x) = \frac{\sqrt{2}}{{\sqrt{2}}^{2}}$

Step 6.2.6

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

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Step 6.2.6.1

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

$\cos (2 x) = \frac{\sqrt{2}}{{(2^{\frac{1}{2}})}^{2}}$

Step 6.2.6.2

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

$\cos (2 x) = \frac{\sqrt{2}}{2^{\frac{1}{2} \cdot 2}}$

Step 6.2.6.3

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

$\cos (2 x) = \frac{\sqrt{2}}{2^{\frac{2}{2}}}$

Step 6.2.6.4

Cancel the common factor of $2$ .

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Step 6.2.6.4.1

Cancel the common factor.

$\cos (2 x) = \frac{\sqrt{2}}{2^{\frac{2}{2}}}$

Step 6.2.6.4.2

Rewrite the expression.

$\cos (2 x) = \frac{\sqrt{2}}{2}$

Step 6.2.6.5

Evaluate the exponent.

$\cos (2 x) = \frac{\sqrt{2}}{2}$

Step 7

Find the value of tangent.

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Step 7.1

Use the definition of tangent to find the value of $\tan (2 x)$ .

$\tan (2 x) = \frac{opp}{adj}$

Step 7.2

Substitute in the known values.

$\tan (2 x) = \frac{1}{1}$

Step 7.3

Divide $1$ by $1$ .

$\tan (2 x) = 1$

Step 8

Find the value of cotangent.

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Step 8.1

Use the definition of cotangent to find the value of $\cot (2 x)$ .

$\cot (2 x) = \frac{adj}{opp}$

Step 8.2

Substitute in the known values.

$\cot (2 x) = \frac{1}{1}$

Step 8.3

Divide $1$ by $1$ .

$\cot (2 x) = 1$

Step 9

Find the value of secant.

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Step 9.1

Use the definition of secant to find the value of $\sec (2 x)$ .

$\sec (2 x) = \frac{hyp}{adj}$

Step 9.2

Substitute in the known values.

$\sec (2 x) = \frac{\sqrt{2}}{1}$

Step 9.3

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

$\sec (2 x) = \sqrt{2}$

Step 10

Find the value of cosecant.

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Step 10.1

Use the definition of cosecant to find the value of $\csc (2 x)$ .

$\csc (2 x) = \frac{hyp}{opp}$

Step 10.2

Substitute in the known values.

$\csc (2 x) = \frac{\sqrt{2}}{1}$

Step 10.3

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

$\csc (2 x) = \sqrt{2}$

Step 11

This is the solution to each trig value.

$\sin (2 x) = \frac{\sqrt{2}}{2}$

$\cos (2 x) = \frac{\sqrt{2}}{2}$

$\tan (2 x) = 1$

$\cot (2 x) = 1$

$\sec (2 x) = \sqrt{2}$

$\csc (2 x) = \sqrt{2}$