Trigonometry Examples

$\cos (θ) = - \frac{3}{5}$

Step 1

Take the inverse cosine of both sides of the equation to extract $θ$ from inside the cosine.

$θ = \arccos (- \frac{3}{5})$

Step 2

Simplify the right side.

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Step 2.1

Evaluate $\arccos (- \frac{3}{5})$ .

$θ = 2.21429743$

Step 3

The cosine function is negative in the second and third quadrants. To find the second solution, subtract the reference angle from $2 π$ to find the solution in the third quadrant.

$θ = 2 (3.14159265) - 2.21429743$

Step 4

Solve for $θ$ .

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Step 4.1

Remove parentheses.

$θ = 2 (3.14159265) - 2.21429743$

Step 4.2

Simplify $2 (3.14159265) - 2.21429743$ .

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Step 4.2.1

Multiply $2$ by $3.14159265$ .

$θ = 6.2831853 - 2.21429743$

Step 4.2.2

Subtract $2.21429743$ from $6.2831853$ .

$θ = 4.06888787$

Step 5

Find the period of $\cos (θ)$ .

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Step 5.1

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

$\frac{2 π}{| b |}$

Step 5.2

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

$\frac{2 π}{| 1 |}$

Step 5.3

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

$\frac{2 π}{1}$

Step 5.4

Divide $2 π$ by $1$ .

$2 π$

Step 6

The period of the $\cos (θ)$ function is $2 π$ so values will repeat every $2 π$ radians in both directions.

$θ = 2.21429743 + 2 π n, 4.06888787 + 2 π n$ , for any integer $n$