Trigonometry Examples

$3 \sin^{2} (x) - 7 \sin (x) + 2 = 0$

Step 1

Factor the left side of the equation.

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Step 1.1

Let $u = \sin (x)$ . Substitute $u$ for all occurrences of $\sin (x)$ .

$3 u^{2} - 7 u + 2 = 0$

Step 1.2

Factor by grouping.

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Step 1.2.1

For a polynomial of the form $a x^{2} + b x + c$ , rewrite the middle term as a sum of two terms whose product is $a \cdot c = 3 \cdot 2 = 6$ and whose sum is $b = - 7$ .

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Step 1.2.1.1

Factor $- 7$ out of $- 7 u$ .

$3 u^{2} - 7 u + 2 = 0$

Step 1.2.1.2

Rewrite $- 7$ as $- 1$ plus $- 6$

$3 u^{2} + (- 1 - 6) u + 2 = 0$

Step 1.2.1.3

Apply the distributive property.

$3 u^{2} - 1 u - 6 u + 2 = 0$

Step 1.2.2

Factor out the greatest common factor from each group.

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Step 1.2.2.1

Group the first two terms and the last two terms.

$(3 u^{2} - 1 u) - 6 u + 2 = 0$

Step 1.2.2.2

Factor out the greatest common factor (GCF) from each group.

$u (3 u - 1) - 2 (3 u - 1) = 0$

Step 1.2.3

Factor the polynomial by factoring out the greatest common factor, $3 u - 1$ .

$(3 u - 1) (u - 2) = 0$

Step 1.3

Replace all occurrences of $u$ with $\sin (x)$ .

$(3 \sin (x) - 1) (\sin (x) - 2) = 0$

Step 2

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

$3 \sin (x) - 1 = 0$

$\sin (x) - 2 = 0$

Step 3

Set $3 \sin (x) - 1$ equal to $0$ and solve for $x$ .

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Step 3.1

Set $3 \sin (x) - 1$ equal to $0$ .

$3 \sin (x) - 1 = 0$

Step 3.2

Solve $3 \sin (x) - 1 = 0$ for $x$ .

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Step 3.2.1

Add $1$ to both sides of the equation.

$3 \sin (x) = 1$

Step 3.2.2

Divide each term in $3 \sin (x) = 1$ by $3$ and simplify.

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Step 3.2.2.1

Divide each term in $3 \sin (x) = 1$ by $3$ .

$\frac{3 \sin (x)}{3} = \frac{1}{3}$

Step 3.2.2.2

Simplify the left side.

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Step 3.2.2.2.1

Cancel the common factor of $3$ .

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Step 3.2.2.2.1.1

Cancel the common factor.

$\frac{3 \sin (x)}{3} = \frac{1}{3}$

Step 3.2.2.2.1.2

Divide $\sin (x)$ by $1$ .

$\sin (x) = \frac{1}{3}$

Step 3.2.3

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

$x = \arcsin (\frac{1}{3})$

Step 3.2.4

Simplify the right side.

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Step 3.2.4.1

Evaluate $\arcsin (\frac{1}{3})$ .

$x = 0.3398369$

Step 3.2.5

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.

$x = (3.14159265) - 0.3398369$

Step 3.2.6

Solve for $x$ .

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Step 3.2.6.1

Remove parentheses.

$x = 3.14159265 - 0.3398369$

Step 3.2.6.2

Remove parentheses.

$x = (3.14159265) - 0.3398369$

Step 3.2.6.3

Subtract $0.3398369$ from $3.14159265$ .

$x = 2.80175574$

Step 3.2.7

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

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Step 3.2.7.1

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

$\frac{2 π}{| b |}$

Step 3.2.7.2

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

$\frac{2 π}{| 1 |}$

Step 3.2.7.3

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

$\frac{2 π}{1}$

Step 3.2.7.4

Divide $2 π$ by $1$ .

$2 π$

Step 3.2.8

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

$x = 0.3398369 + 2 π n, 2.80175574 + 2 π n$ , for any integer $n$

Step 4

Set $\sin (x) - 2$ equal to $0$ and solve for $x$ .

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Step 4.1

Set $\sin (x) - 2$ equal to $0$ .

$\sin (x) - 2 = 0$

Step 4.2

Solve $\sin (x) - 2 = 0$ for $x$ .

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Step 4.2.1

Add $2$ to both sides of the equation.

$\sin (x) = 2$

Step 4.2.2

The range of sine is $- 1 \leq y \leq 1$ . Since $2$ does not fall in this range, there is no solution.

No solution

Step 5

The final solution is all the values that make $(3 \sin (x) - 1) (\sin (x) - 2) = 0$ true.

$x = 0.3398369 + 2 π n, 2.80175574 + 2 π n$ , for any integer $n$