Trigonometry Examples

$\sin (a - 60) = - \frac{\sqrt{3}}{2}$

Step 1

Take the inverse sine of both sides of the equation to extract $a$ from inside the sine.

$a - 60 = \arcsin (- \frac{\sqrt{3}}{2})$

Step 2

Simplify the right side.

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Step 2.1

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

$a - 60 = - \frac{π}{3}$

Step 3

Add $60$ to both sides of the equation.

$a = - \frac{π}{3} + 60$

Step 4

The sine function is negative in the third and fourth quadrants. To find the second solution, subtract the solution from $2 π$ , to find a reference angle. Next, add this reference angle to $π$ to find the solution in the third quadrant.

$a - 60 = 2 π + \frac{π}{3} + π$

Step 5

Simplify the expression to find the second solution.

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Step 5.1

Subtract $2 π$ from $2 π + \frac{π}{3} + π$ .

$a - 60 = 2 π + \frac{π}{3} + π - 2 π$

Step 5.2

The resulting angle of $\frac{4 π}{3}$ is positive, less than $2 π$ , and coterminal with $2 π + \frac{π}{3} + π$ .

$a - 60 = \frac{4 π}{3}$

Step 5.3

Add $60$ to both sides of the equation.

$a = \frac{4 π}{3} + 60$

Step 6

Find the period of $\sin (a - 60)$ .

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Step 6.1

The period of the function can be calculated using $\frac{2 π}{| b |}$ .

$\frac{2 π}{| b |}$

Step 6.2

Replace $b$ with $1$ in the formula for period.

$\frac{2 π}{| 1 |}$

Step 6.3

The absolute value is the distance between a number and zero. The distance between $0$ and $1$ is $1$ .

$\frac{2 π}{1}$

Step 6.4

Divide $2 π$ by $1$ .

$2 π$

Step 7

Add $2 π$ to every negative angle to get positive angles.

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Step 7.1

Add $2 π$ to $- \frac{π}{3} + 60$ to find the positive angle.

$- \frac{π}{3} + 60 + 2 π$

Step 7.2

To write $2 π$ as a fraction with a common denominator, multiply by $\frac{3}{3}$ .

$2 π \cdot \frac{3}{3} - \frac{π}{3} + 60$

Step 7.3

Combine fractions.

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Step 7.3.1

Combine $2 π$ and $\frac{3}{3}$ .

$\frac{2 π \cdot 3}{3} - \frac{π}{3} + 60$

Step 7.3.2

Combine the numerators over the common denominator.

$\frac{2 π \cdot 3 - π}{3} + 60$

Step 7.4

Simplify the numerator.

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Step 7.4.1

Multiply $3$ by $2$ .

$\frac{6 π - π}{3} + 60$

Step 7.4.2

Subtract $π$ from $6 π$ .

$\frac{5 π}{3} + 60$

Step 7.5

List the new angles.

$a = \frac{5 π}{3} + 60$

Step 8

The period of the $\sin (a - 60)$ function is $2 π$ so values will repeat every $2 π$ radians in both directions.

$a = \frac{4 π}{3} + 60 + 2 π n, \frac{5 π}{3} + 60 + 2 π n$ , for any integer $n$