Precalculus Examples

$\cos (\frac{7 π}{4} + \frac{π}{6})$

Step 1

Use the sum formula for cosine to simplify the expression. The formula states that $\cos (A + B) = - (\cos (A) \cos (B) + \sin (A) \sin (B))$ .

$\cos (\frac{π}{6}) \cdot \cos (\frac{7 π}{4}) - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 2

Remove parentheses.

$\cos (\frac{π}{6}) \cdot \cos (\frac{7 π}{4}) - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3

Simplify each term.

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Step 3.1

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

$\frac{\sqrt{3}}{2} \cdot \cos (\frac{7 π}{4}) - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.2

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

$\frac{\sqrt{3}}{2} \cdot \cos (\frac{π}{4}) - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.3

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

$\frac{\sqrt{3}}{2} \cdot \frac{\sqrt{2}}{2} - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.4

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

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Step 3.4.1

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

$\frac{\sqrt{3} \sqrt{2}}{2 \cdot 2} - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.4.2

Combine using the product rule for radicals.

$\frac{\sqrt{3 \cdot 2}}{2 \cdot 2} - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.4.3

Multiply $3$ by $2$ .

$\frac{\sqrt{6}}{2 \cdot 2} - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.4.4

Multiply $2$ by $2$ .

$\frac{\sqrt{6}}{4} - \sin (\frac{π}{6}) \cdot \sin (\frac{7 π}{4})$

Step 3.5

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

$\frac{\sqrt{6}}{4} - \frac{1}{2} \cdot \sin (\frac{7 π}{4})$

Step 3.6

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 fourth quadrant.

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

Step 3.7

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

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

Step 3.8

Multiply $- \frac{1}{2} (- \frac{\sqrt{2}}{2})$ .

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Step 3.8.1

Multiply $- 1$ by $- 1$ .

$\frac{\sqrt{6}}{4} + 1 (\frac{1}{2}) \frac{\sqrt{2}}{2}$

Step 3.8.2

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

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

Step 3.8.3

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

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

Step 3.8.4

Multiply $2$ by $2$ .

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

Step 4

Combine the numerators over the common denominator.

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

Step 5

The result can be shown in multiple forms.

Exact Form:

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

Decimal Form:

$0.96592582 \dots$