What is the general solution for sin(x/2)+sin(x/2)=sin(x) ?

The general solution for sin(x/2)+sin(x/2)=sin(x) is x=4pin,x=2pi+4pin

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sin(x/2)+sin(x/2)=sin(x)

Solution

sin (\frac{x}{2}) + sin (\frac{x}{2}) = sin (x)

Solution

x = 4 πn, x = 2 π + 4 πn

Degrees

x = 0^{\circ} + 72 0^{\circ} n, x = 36 0^{\circ} + 72 0^{\circ} n

Solution steps

sin (\frac{x}{2}) + sin (\frac{x}{2}) = sin (x)

Subtract

sin (x)

from both sides

2 sin (\frac{x}{2}) - sin (x) = 0

Let:

u = \frac{x}{2}

2 sin (u) - sin (2 u) = 0

Rewrite using trig identities

- sin (2 u) + 2 sin (u)

Use the Double Angle identity:

sin (2 x) = 2 sin (x) cos (x)

= - 2 sin (u) cos (u) + 2 sin (u)

2 sin (u) - 2 cos (u) sin (u) = 0

Factor

2 sin (u) - 2 cos (u) sin (u) : - 2 sin (u) (cos (u) - 1)

2 sin (u) - 2 cos (u) sin (u)

Factor out common term

- 2 sin (u)

= - 2 sin (u) (- 1 + cos (u))

- 2 sin (u) (cos (u) - 1) = 0

Solving each part separately

sin (u) = 0 or cos (u) - 1 = 0

sin (u) = 0 : u = 2 πn, u = π + 2 πn

sin (u) = 0

General solutions for

sin (u) = 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}

u = 0 + 2 πn, u = π + 2 πn

u = 0 + 2 πn, u = π + 2 πn

Solve

u = 0 + 2 πn : u = 2 πn

u = 0 + 2 πn

0 + 2 πn = 2 πn

u = 2 πn

u = 2 πn, u = π + 2 πn

cos (u) - 1 = 0 : u = 2 πn

cos (u) - 1 = 0

Move

1

to the right side

cos (u) - 1 = 0

Add

1

to both sides

cos (u) - 1 + 1 = 0 + 1

Simplify

cos (u) = 1

cos (u) = 1

General solutions for

cos (u) = 1

cos (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} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{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} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

u = 0 + 2 πn

u = 0 + 2 πn

Solve

u = 0 + 2 πn : u = 2 πn

u = 0 + 2 πn

0 + 2 πn = 2 πn

u = 2 πn

u = 2 πn

Combine all the solutions

u = 2 πn, u = π + 2 πn

Substitute back

u = \frac{x}{2}

\frac{x}{2} = 2 πn : x = 4 πn

\frac{x}{2} = 2 πn

Multiply both sides by

2

\frac{x}{2} = 2 πn

Multiply both sides by

2

\frac{2 x}{2} = 2 \cdot 2 πn

Simplify

x = 4 πn

x = 4 πn

\frac{x}{2} = π + 2 πn : x = 2 π + 4 πn

\frac{x}{2} = π + 2 πn

Multiply both sides by

2

\frac{x}{2} = π + 2 πn

Multiply both sides by

2

\frac{2 x}{2} = 2 π + 2 \cdot 2 πn

Simplify

x = 2 π + 4 πn

x = 2 π + 4 πn

x = 4 πn, x = 2 π + 4 πn

Popular Examples

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cos (x) + 2 sin^{2} (x) = 1

15cos(x)-5=4cos(x)

15 cos (x) - 5 = 4 cos (x)

sin(θ)+cos(θ)=sqrt((2+\sqrt{3))/2}

sin (θ) + cos (θ) = \frac{2 + 3}{2}

solvefor x,arctan(1/x)=80 solve for

x, arctan (\frac{1}{x}) = 8 0^{\circ}

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2 sin (θ) cos (θ) + 2 sin (θ) + cos (θ) + 1 = 0

Frequently Asked Questions (FAQ)

What is the general solution for sin(x/2)+sin(x/2)=sin(x) ?
The general solution for sin(x/2)+sin(x/2)=sin(x) is x=4pin,x=2pi+4pin