Trigonometry Examples

\cos (x) = \frac{5}{7}

$\cos (x) = \frac{5}{7}$

Step 1

Take the inverse cosine of both sides of the equation to extract

x

$x$ from inside the cosine.

x = \arccos (\frac{5}{7})

$x = \arccos (\frac{5}{7})$

Step 2

Simplify the right side.

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Step 2.1

Evaluate

\arccos (\frac{5}{7})

$\arccos (\frac{5}{7})$ .

x = 0.77519337

$x = 0.77519337$

x = 0.77519337

$x = 0.77519337$

Step 3

The cosine function is positive in the first and fourth quadrants. To find the second solution, subtract the reference angle from

2 π

$2 π$ to find the solution in the fourth quadrant.

x = 2 (3.14159265) - 0.77519337

$x = 2 (3.14159265) - 0.77519337$

Step 4

Simplify

2 (3.14159265) - 0.77519337

$2 (3.14159265) - 0.77519337$ .

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Step 4.1

Multiply

2

$2$ by

3.14159265

$3.14159265$ .

x = 6.2831853 - 0.77519337

$x = 6.2831853 - 0.77519337$

Step 4.2

Subtract

0.77519337

$0.77519337$ from

6.2831853

$6.2831853$ .

x = 5.50799193

$x = 5.50799193$

x = 5.50799193

$x = 5.50799193$

Step 5

Find the period of

\cos (x)

$\cos (x)$ .

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Step 5.1

The period of the function can be calculated using

\frac{2 π}{| b |}

$\frac{2 π}{| b |}$ .

\frac{2 π}{| b |}

$\frac{2 π}{| b |}$

Step 5.2

Replace

b

$b$ with

1

$1$ in the formula for period.

\frac{2 π}{| 1 |}

$\frac{2 π}{| 1 |}$

Step 5.3

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

0

$0$ and

1

$1$ is

1

$1$ .

\frac{2 π}{1}

$\frac{2 π}{1}$

Step 5.4

Divide

2 π

$2 π$ by

1

$1$ .

2 π

$2 π$

2 π

$2 π$

Step 6

The period of the

\cos (x)

$\cos (x)$ function is

2 π

$2 π$ so values will repeat every

2 π

$2 π$ radians in both directions.

x = 0.77519337 + 2 π n, 5.50799193 + 2 π n

$x = 0.77519337 + 2 π n, 5.50799193 + 2 π n$ , for any integer

n

$n$

\cos (x) = \frac{5}{7}

$\cos (x) = \frac{5}{7}$

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