Trigonometry Examples

$\tan^{2} (x) - 4 \sec (x) = 4$

Step 1

Replace the $\tan^{2} (x)$ with $\sec^{2} (x) - 1$ based on the $\tan^{2} (x) + 1 = \sec^{2} (x)$ identity.

$(\sec^{2} (x) - 1) - 4 \sec (x) = 4$

Step 2

Reorder the polynomial.

$\sec^{2} (x) - 4 \sec (x) - 1 = 4$

Step 3

Substitute $u$ for $\sec (x)$ .

${(u)}^{2} - 4 u - 1 = 4$

Step 4

Subtract $4$ from both sides of the equation.

$u^{2} - 4 u - 1 - 4 = 0$

Step 5

Subtract $4$ from $- 1$ .

$u^{2} - 4 u - 5 = 0$

Step 6

Factor $u^{2} - 4 u - 5$ using the AC method.

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Step 6.1

Consider the form $x^{2} + b x + c$ . Find a pair of integers whose product is $c$ and whose sum is $b$ . In this case, whose product is $- 5$ and whose sum is $- 4$ .

$- 5, 1$

Step 6.2

Write the factored form using these integers.

$(u - 5) (u + 1) = 0$

Step 7

If any individual factor on the left side of the equation is equal to $0$ , the entire expression will be equal to $0$ .

$u - 5 = 0$

$u + 1 = 0$

Step 8

Set $u - 5$ equal to $0$ and solve for $u$ .

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Step 8.1

Set $u - 5$ equal to $0$ .

$u - 5 = 0$

Step 8.2

Add $5$ to both sides of the equation.

$u = 5$

Step 9

Set $u + 1$ equal to $0$ and solve for $u$ .

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Step 9.1

Set $u + 1$ equal to $0$ .

$u + 1 = 0$

Step 9.2

Subtract $1$ from both sides of the equation.

$u = - 1$

Step 10

The final solution is all the values that make $(u - 5) (u + 1) = 0$ true.

$u = 5, - 1$

Step 11

Substitute $\sec (x)$ for $u$ .

$\sec (x) = 5, - 1$

Step 12

Set up each of the solutions to solve for $x$ .

$\sec (x) = 5$

$\sec (x) = - 1$

Step 13

Solve for $x$ in $\sec (x) = 5$ .

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Step 13.1

Take the inverse secant of both sides of the equation to extract $x$ from inside the secant.

$x = arcsec (5)$

Step 13.2

Simplify the right side.

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Step 13.2.1

Evaluate $arcsec (5)$ .

$x = 1.3694384$

Step 13.3

The secant function is positive in the first and fourth quadrants. To find the second solution, subtract the reference angle from $2 π$ to find the solution in the fourth quadrant.

$x = 2 (3.14159265) - 1.3694384$

Step 13.4

Solve for $x$ .

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Step 13.4.1

Remove parentheses.

$x = 2 (3.14159265) - 1.3694384$

Step 13.4.2

Simplify $2 (3.14159265) - 1.3694384$ .

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Step 13.4.2.1

Multiply $2$ by $3.14159265$ .

$x = 6.2831853 - 1.3694384$

Step 13.4.2.2

Subtract $1.3694384$ from $6.2831853$ .

$x = 4.9137469$

Step 13.5

Find the period of $\sec (x)$ .

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Step 13.5.1

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

$\frac{2 π}{| b |}$

Step 13.5.2

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

$\frac{2 π}{| 1 |}$

Step 13.5.3

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

$\frac{2 π}{1}$

Step 13.5.4

Divide $2 π$ by $1$ .

$2 π$

Step 13.6

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

$x = 1.3694384 + 2 π n, 4.9137469 + 2 π n$ , for any integer $n$

Step 14

Solve for $x$ in $\sec (x) = - 1$ .

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Step 14.1

Take the inverse secant of both sides of the equation to extract $x$ from inside the secant.

$x = arcsec (- 1)$

Step 14.2

Simplify the right side.

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Step 14.2.1

The exact value of $arcsec (- 1)$ is $π$ .

$x = π$

Step 14.3

The secant 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.

$x = 2 π - π$

Step 14.4

Subtract $π$ from $2 π$ .

$x = π$

Step 14.5

Find the period of $\sec (x)$ .

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Step 14.5.1

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

$\frac{2 π}{| b |}$

Step 14.5.2

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

$\frac{2 π}{| 1 |}$

Step 14.5.3

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

$\frac{2 π}{1}$

Step 14.5.4

Divide $2 π$ by $1$ .

$2 π$

Step 14.6

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

$x = π + 2 π n$ , for any integer $n$

Step 15

List all of the solutions.

$x = 1.3694384 + 2 π n, 4.9137469 + 2 π n, π + 2 π n$ , for any integer $n$