What is the general solution for 3sin^2(x)+2sin(x)-1=0 ?

The general solution for 3sin^2(x)+2sin(x)-1=0 is x=0.33983…+2pin,x=pi-0.33983…+2pin,x=(3pi)/2+2pin

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3sin^2(x)+2sin(x)-1=0

Solution

3 sin^{2} (x) + 2 sin (x) - 1 = 0

Solution

x = 0.33983 \dots + 2 πn, x = π - 0.33983 \dots + 2 πn, x = \frac{3 π}{2} + 2 πn

Degrees

x = 19.47122 \dots^{\circ} + 36 0^{\circ} n, x = 160.52877 \dots^{\circ} + 36 0^{\circ} n, x = 27 0^{\circ} + 36 0^{\circ} n

Solution steps

3 sin^{2} (x) + 2 sin (x) - 1 = 0

Solve by substitution

3 sin^{2} (x) + 2 sin (x) - 1 = 0

Let:

sin (x) = u

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

3 u^{2} + 2 u - 1 = 0 : u = \frac{1}{3}, u = - 1

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

Solve with the quadratic formula

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

Quadratic Equation Formula:

For

a = 3, b = 2, c = - 1

u_{1, 2} = \frac{- 2 \pm 2 ^{2} - 4 \cdot 3 ( - 1 )}{2 \cdot 3}

u_{1, 2} = \frac{- 2 \pm 2 ^{2} - 4 \cdot 3 ( - 1 )}{2 \cdot 3}

2^{2} - 4 \cdot 3 (- 1) = 4

2^{2} - 4 \cdot 3 (- 1)

Apply rule

- (- a) = a

= 2^{2} + 4 \cdot 3 \cdot 1

Multiply the numbers:

4 \cdot 3 \cdot 1 = 12

= 2^{2} + 12

2^{2} = 4

= 4 + 12

Add the numbers:

4 + 12 = 16

= 16

Factor the number:

16 = 4^{2}

= 4^{2}

Apply radical rule:

4^{2} = 4

= 4

u_{1, 2} = \frac{- 2 \pm 4}{2 \cdot 3}

Separate the solutions

u_{1} = \frac{- 2 + 4}{2 \cdot 3}, u_{2} = \frac{- 2 - 4}{2 \cdot 3}

u = \frac{- 2 + 4}{2 \cdot 3} : \frac{1}{3}

\frac{- 2 + 4}{2 \cdot 3}

Add/Subtract the numbers:

- 2 + 4 = 2

= \frac{2}{2 \cdot 3}

Multiply the numbers:

2 \cdot 3 = 6

= \frac{2}{6}

Cancel the common factor:

2

= \frac{1}{3}

u = \frac{- 2 - 4}{2 \cdot 3} : - 1

\frac{- 2 - 4}{2 \cdot 3}

Subtract the numbers:

- 2 - 4 = - 6

= \frac{- 6}{2 \cdot 3}

Multiply the numbers:

2 \cdot 3 = 6

= \frac{- 6}{6}

Apply the fraction rule:

\frac{- a}{b} = - \frac{a}{b}

= - \frac{6}{6}

Apply rule

\frac{a}{a} = 1

= - 1

The solutions to the quadratic equation are:

u = \frac{1}{3}, u = - 1

Substitute back

u = sin (x)

sin (x) = \frac{1}{3}, sin (x) = - 1

sin (x) = \frac{1}{3}, sin (x) = - 1

sin (x) = \frac{1}{3} : x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn

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

Apply trig inverse properties

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

General solutions for

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

sin (x) = a \Rightarrow x = arcsin (a) + 2 πn, x = π - arcsin (a) + 2 πn

x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn

x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn

sin (x) = - 1 : x = \frac{3 π}{2} + 2 πn

sin (x) = - 1

General solutions for

sin (x) = - 1

sin (x)

periodicity table with

2 πn

cycle:

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

x = \frac{3 π}{2} + 2 πn

x = \frac{3 π}{2} + 2 πn

Combine all the solutions

x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn, x = \frac{3 π}{2} + 2 πn

Show solutions in decimal form

x = 0.33983 \dots + 2 πn, x = π - 0.33983 \dots + 2 πn, x = \frac{3 π}{2} + 2 πn

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Frequently Asked Questions (FAQ)

What is the general solution for 3sin^2(x)+2sin(x)-1=0 ?
The general solution for 3sin^2(x)+2sin(x)-1=0 is x=0.33983…+2pin,x=pi-0.33983…+2pin,x=(3pi)/2+2pin