What is the general solution for sin(a)+sin(120+a)+sin(120-a)=0 ?

The general solution for sin(a)+sin(120+a)+sin(120-a)=0 is a=120+180n

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Popular Trigonometry >

sin(a)+sin(120+a)+sin(120-a)=0

Solution

sin (a) + sin (12 0^{\circ} + a) + sin (12 0^{\circ} - a) = 0

Solution

a = 12 0^{\circ} + 18 0^{\circ} n

Radians

a = \frac{2 π}{3} + πn

Solution steps

sin (a) + sin (12 0^{\circ} + a) + sin (12 0^{\circ} - a) = 0

Rewrite using trig identities

sin (a) + sin (12 0^{\circ} + a) + sin (12 0^{\circ} - a) = 0

Rewrite using trig identities

sin (12 0^{\circ} + a)

Use the Angle Sum identity:

sin (s + t) = sin (s) cos (t) + cos (s) sin (t)

= sin (12 0^{\circ}) cos (a) + cos (12 0^{\circ}) sin (a)

Simplify

sin (12 0^{\circ}) cos (a) + cos (12 0^{\circ}) sin (a) : \frac{3}{2} cos (a) - \frac{1}{2} sin (a)

sin (12 0^{\circ}) cos (a) + cos (12 0^{\circ}) sin (a)

Simplify

sin (12 0^{\circ}) : \frac{3}{2}

sin (12 0^{\circ})

Use the following trivial identity:

sin (12 0^{\circ}) = \frac{3}{2}

sin (x)

periodicity table with

36 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= \frac{3}{2}

= \frac{3}{2} cos (a) + cos (12 0^{\circ}) sin (a)

Simplify

cos (12 0^{\circ}) : - \frac{1}{2}

cos (12 0^{\circ})

Use the following trivial identity:

cos (12 0^{\circ}) = - \frac{1}{2}

cos (x)

periodicity table with

36 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= - \frac{1}{2}

= \frac{3}{2} cos (a) - \frac{1}{2} sin (a)

= \frac{3}{2} cos (a) - \frac{1}{2} sin (a)

Use the Angle Difference identity:

sin (s - t) = sin (s) cos (t) - cos (s) sin (t)

= sin (12 0^{\circ}) cos (a) - cos (12 0^{\circ}) sin (a)

Simplify

sin (12 0^{\circ}) cos (a) - cos (12 0^{\circ}) sin (a) : \frac{3}{2} cos (a) + \frac{1}{2} sin (a)

sin (12 0^{\circ}) cos (a) - cos (12 0^{\circ}) sin (a)

Simplify

sin (12 0^{\circ}) : \frac{3}{2}

sin (12 0^{\circ})

Use the following trivial identity:

sin (12 0^{\circ}) = \frac{3}{2}

sin (x)

periodicity table with

36 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= \frac{3}{2}

= \frac{3}{2} cos (a) - cos (12 0^{\circ}) sin (a)

Simplify

cos (12 0^{\circ}) : - \frac{1}{2}

cos (12 0^{\circ})

Use the following trivial identity:

cos (12 0^{\circ}) = - \frac{1}{2}

cos (x)

periodicity table with

36 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= - \frac{1}{2}

= \frac{3}{2} cos (a) - (- \frac{1}{2} sin (a))

Apply rule

- (- a) = a

= \frac{3}{2} cos (a) + \frac{1}{2} sin (a)

= \frac{3}{2} cos (a) + \frac{1}{2} sin (a)

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

Simplify

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

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

Group like terms

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

Add similar elements:

\frac{3}{2} cos (a) + \frac{3}{2} cos (a) = 3 cos (a)

\frac{3}{2} cos (a) + \frac{3}{2} cos (a)

Factor out common term

cos (a)

= cos (a) (\frac{3}{2} + \frac{3}{2})

\frac{3}{2} + \frac{3}{2} = 3

\frac{3}{2} + \frac{3}{2}

Apply rule

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

= \frac{3 + 3}{2}

Factor

3 + 3 : 23

3 + 3

Factor out common term

3

= 3 (1 + 1)

Refine

= 23

= \frac{2 3}{2}

Divide the numbers:

\frac{2}{2} = 1

= 3

= 3 cos (a)

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

Add similar elements:

- \frac{1}{2} sin (a) + \frac{1}{2} sin (a) + sin (a) = sin (a)

- \frac{1}{2} sin (a) + \frac{1}{2} sin (a) + sin (a)

Factor out common term

sin (a)

= sin (a) (- \frac{1}{2} + \frac{1}{2} + 1)

- \frac{1}{2} + \frac{1}{2} + 1 = 1

- \frac{1}{2} + \frac{1}{2} + 1

Convert element to fraction:

1 = \frac{1}{1}

= - \frac{1}{2} + \frac{1}{2} + \frac{1}{1}

Least Common Multiplier of

2, 2, 1 : 2

2, 2, 1

Least Common Multiplier (LCM)

Prime factorization of

2 : 2

2

2

is a prime number, therefore no factorization is possible

= 2

Prime factorization of

2 : 2

2

2

is a prime number, therefore no factorization is possible

= 2

Prime factorization of

1

Compute a number comprised of factors that appear in at least one of the following:

2, 2, 1

= 2

Multiply the numbers:

2 = 2

= 2

Adjust Fractions based on the LCM

Multiply each numerator by the same amount needed to multiply its

corresponding denominator to turn it into the LCM

2

For

\frac{1}{1} :

multiply the denominator and numerator by

2

\frac{1}{1} = \frac{1 \cdot 2}{1 \cdot 2} = \frac{2}{2}

= - \frac{1}{2} + \frac{1}{2} + \frac{2}{2}

Since the denominators are equal, combine the fractions:

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

= \frac{- 1 + 1 + 2}{2}

Refine

= 1

= sin (a)

= sin (a) + 3 cos (a)

sin (a) + 3 cos (a) = 0

Divide both sides by

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

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

Simplify

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

Use the basic trigonometric identity:

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

tan (a) + 3 = 0

tan (a) + 3 = 0

Move

3

to the right side

tan (a) + 3 = 0

Subtract

3

from both sides

tan (a) + 3 - 3 = 0 - 3

Simplify

tan (a) = - 3

tan (a) = - 3

General solutions for

tan (a) = - 3

tan (x)

periodicity table with

18 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} tan (x) 0 \frac{3}{3} 13 \pm \infty - 3 - 1 - \frac{3}{3}

a = 12 0^{\circ} + 18 0^{\circ} n

a = 12 0^{\circ} + 18 0^{\circ} n

Graph

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Frequently Asked Questions (FAQ)

What is the general solution for sin(a)+sin(120+a)+sin(120-a)=0 ?
The general solution for sin(a)+sin(120+a)+sin(120-a)=0 is a=120+180n