Precalculus Examples

$\sin^{2} (x) - \cos^{2} (x) = - 1$

Step 1

Add $1$ to both sides of the equation.

$\sin^{2} (x) - \cos^{2} (x) + 1 = 0$

Step 2

Simplify $\sin^{2} (x) - \cos^{2} (x) + 1$ .

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Step 2.1

Reorder $- \cos^{2} (x)$ and $1$ .

$\sin^{2} (x) + 1 - \cos^{2} (x) = 0$

Step 2.2

Apply pythagorean identity.

$\sin^{2} (x) + \sin^{2} (x) = 0$

Step 2.3

Add $\sin^{2} (x)$ and $\sin^{2} (x)$ .

$2 \sin^{2} (x) = 0$

Step 3

Solve for $x$ .

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Step 3.1

Divide each term in $2 \sin^{2} (x) = 0$ by $2$ and simplify.

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Step 3.1.1

Divide each term in $2 \sin^{2} (x) = 0$ by $2$ .

$\frac{2 \sin^{2} (x)}{2} = \frac{0}{2}$

Step 3.1.2

Simplify the left side.

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Step 3.1.2.1

Cancel the common factor of $2$ .

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Step 3.1.2.1.1

Cancel the common factor.

$\frac{2 \sin^{2} (x)}{2} = \frac{0}{2}$

Step 3.1.2.1.2

Divide $\sin^{2} (x)$ by $1$ .

$\sin^{2} (x) = \frac{0}{2}$

Step 3.1.3

Simplify the right side.

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Step 3.1.3.1

Divide $0$ by $2$ .

$\sin^{2} (x) = 0$

Step 3.2

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$\sin (x) = \pm \sqrt{0}$

Step 3.3

Simplify $\pm \sqrt{0}$ .

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Step 3.3.1

Rewrite $0$ as $0^{2}$ .

$\sin (x) = \pm \sqrt{0^{2}}$

Step 3.3.2

Pull terms out from under the radical, assuming positive real numbers.

$\sin (x) = \pm 0$

Step 3.3.3

Plus or minus $0$ is $0$ .

$\sin (x) = 0$

Step 3.4

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

$x = \arcsin (0)$

Step 3.5

Simplify the right side.

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Step 3.5.1

The exact value of $\arcsin (0)$ is $0$ .

$x = 0$

Step 3.6

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

$x = π - 0$

Step 3.7

Subtract $0$ from $π$ .

$x = π$

Step 3.8

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

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Step 3.8.1

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

$\frac{2 π}{| b |}$

Step 3.8.2

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

$\frac{2 π}{| 1 |}$

Step 3.8.3

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

$\frac{2 π}{1}$

Step 3.8.4

Divide $2 π$ by $1$ .

$2 π$

Step 3.9

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

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

Step 4

Consolidate the answers.

$x = π n$ , for any integer $n$