Solve for x sin(x)^2+cos(x)=0

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

Replace $\sin^{2} (x)$ with $1 - \cos^{2} (x)$ .

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

Solve for $x$ .

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

$1 - {(u)}^{2} + u = 0$

Use the quadratic formula to find the solutions.

$\frac{- b \pm \sqrt{b^{2} - 4 (a c)}}{2 a}$

Substitute the values $a = - 1$ , $b = 1$ , and $c = 1$ into the quadratic formula and solve for $u$ .

$\frac{- 1 \pm \sqrt{1^{2} - 4 \cdot (- 1 \cdot 1)}}{2 \cdot - 1}$

Simplify.

Simplify the numerator.

One to any power is one.

$u = \frac{- 1 \pm \sqrt{1 - 4 \cdot - 1 \cdot 1}}{2 \cdot - 1}$

Multiply $- 4$ by $- 1$ .

$u = \frac{- 1 \pm \sqrt{1 + 4 \cdot 1}}{2 \cdot - 1}$

Multiply $4$ by $1$ .

$u = \frac{- 1 \pm \sqrt{1 + 4}}{2 \cdot - 1}$

Add $1$ and $4$ .

$u = \frac{- 1 \pm \sqrt{5}}{2 \cdot - 1}$

Multiply $2$ by $- 1$ .

$u = \frac{- 1 \pm \sqrt{5}}{- 2}$

Simplify $\frac{- 1 \pm \sqrt{5}}{- 2}$ .

$u = \frac{1 \pm \sqrt{5}}{2}$

The final answer is the combination of both solutions.

$u = \frac{1 + \sqrt{5}}{2}, \frac{1 - \sqrt{5}}{2}$

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

$\cos (x) = \frac{1 + \sqrt{5}}{2}, \frac{1 - \sqrt{5}}{2}$

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

$\cos (x) = \frac{1 + \sqrt{5}}{2}$

$\cos (x) = \frac{1 - \sqrt{5}}{2}$

Solve for $x$ in $\cos (x) = \frac{1 + \sqrt{5}}{2}$ .

The range of cosine is $- 1 \leq y \leq 1$ . Since $\frac{1 + \sqrt{5}}{2}$ does not fall in this range, there is no solution.

No solution

Solve for $x$ in $\cos (x) = \frac{1 - \sqrt{5}}{2}$ .

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

$x = \arccos (\frac{1 - \sqrt{5}}{2})$

Simplify the right side.

Evaluate $\arccos (\frac{1 - \sqrt{5}}{2})$ .

$x = 2.23703575$

The cosine 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.

$x = 2 (3.14159265) - 2.23703575$

Solve for $x$ .

Remove parentheses.

$x = 2 (3.14159265) - 2.23703575$

Simplify $2 (3.14159265) - 2.23703575$ .

Multiply $2$ by $3.14159265$ .

$x = 6.2831853 - 2.23703575$

Subtract $2.23703575$ from $6.2831853$ .

$x = 4.04614954$

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

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

$\frac{2 π}{| b |}$

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

$\frac{2 π}{| 1 |}$

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

$\frac{2 π}{1}$

Divide $2 π$ by $1$ .

$2 π$

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

$x = 2.23703575 + 2 π n, 4.04614954 + 2 π n$ , for any integer $n$

List all of the solutions.

$x = 2.23703575 + 2 π n, 4.04614954 + 2 π n$ , for any integer $n$

Solve for x sin(x)^2+cos(x)=0

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