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

The general solution for 3sin^2(x)+2sin(x)cos^2(x/2)-sin(x)=0 is x=2pin,x=pi+2pin,x=-0.32175…+pin

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3sin^2(x)+2sin(x)cos^2(x/2)-sin(x)=0

Solution

3 sin^{2} (x) + 2 sin (x) cos^{2} (\frac{x}{2}) - sin (x) = 0

Solution

x = 2 πn, x = π + 2 πn, x = - 0.32175 \dots + πn

Degrees

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = - 18.43494 \dots^{\circ} + 18 0^{\circ} n

Solution steps

3 sin^{2} (x) + 2 sin (x) cos^{2} (\frac{x}{2}) - sin (x) = 0

Factor

3 sin^{2} (x) + 2 sin (x) cos^{2} (\frac{x}{2}) - sin (x) : sin (x) (3 sin (x) + 2 cos^{2} (\frac{x}{2}) - 1)

3 sin^{2} (x) + 2 sin (x) cos^{2} (\frac{x}{2}) - sin (x)

Apply exponent rule:

a^{b + c} = a^{b} a^{c}

sin^{2} (x) = sin (x) sin (x)

= 3 sin (x) sin (x) + 2 sin (x) cos^{2} (\frac{x}{2}) - sin (x)

Factor out common term

sin (x)

= sin (x) (3 sin (x) + 2 cos^{2} (\frac{x}{2}) - 1)

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

Solving each part separately

sin (x) = 0 or 3 sin (x) + 2 cos^{2} (\frac{x}{2}) - 1 = 0

sin (x) = 0 : x = 2 πn, x = π + 2 πn

sin (x) = 0

General solutions for

sin (x) = 0

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 = 0 + 2 πn, x = π + 2 πn

x = 0 + 2 πn, x = π + 2 πn

Solve

x = 0 + 2 πn : x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn, x = π + 2 πn

3 sin (x) + 2 cos^{2} (\frac{x}{2}) - 1 = 0 : x = arctan (- \frac{1}{3}) + πn

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

Rewrite using trig identities

- 1 + 2 cos^{2} (\frac{x}{2}) + 3 sin (x)

Use the Double Angle identity:

2 cos^{2} (x) - 1 = cos (2 x)

= 3 sin (x) + cos (2 \cdot \frac{x}{2})

Multiply

2 \cdot \frac{x}{2} : x

2 \cdot \frac{x}{2}

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{x \cdot 2}{2}

Cancel the common factor:

2

= x

= 3 sin (x) + cos (x)

Divide both sides by

cos (x), cos (x) \neq = 0

\frac{cos ( x ) + 3 sin ( x )}{cos ( x )} = \frac{0}{cos ( x )}

Simplify

1 + \frac{3 sin ( x )}{cos ( x )} = 0

Use the basic trigonometric identity:

\frac{sin ( x )}{cos ( x )} = tan (x)

1 + 3 tan (x) = 0

1 + 3 tan (x) = 0

Move

1

to the right side

1 + 3 tan (x) = 0

Subtract

1

from both sides

1 + 3 tan (x) - 1 = 0 - 1

Simplify

3 tan (x) = - 1

3 tan (x) = - 1

Divide both sides by

3

3 tan (x) = - 1

Divide both sides by

3

\frac{3 tan ( x )}{3} = \frac{- 1}{3}

Simplify

tan (x) = - \frac{1}{3}

tan (x) = - \frac{1}{3}

Apply trig inverse properties

tan (x) = - \frac{1}{3}

General solutions for

tan (x) = - \frac{1}{3}

tan (x) = - a \Rightarrow x = arctan (- a) + πn

x = arctan (- \frac{1}{3}) + πn

x = arctan (- \frac{1}{3}) + πn

Combine all the solutions

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

Show solutions in decimal form

x = 2 πn, x = π + 2 πn, x = - 0.32175 \dots + πn

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Frequently Asked Questions (FAQ)

What is the general solution for 3sin^2(x)+2sin(x)cos^2(x/2)-sin(x)=0 ?
The general solution for 3sin^2(x)+2sin(x)cos^2(x/2)-sin(x)=0 is x=2pin,x=pi+2pin,x=-0.32175…+pin