What is the general solution for 2sin(6x)+2sin(2x)=0 ?

The general solution for 2sin(6x)+2sin(2x)=0 is x=pin,x=(pi+2pin)/2 ,x=(3pi+4pin)/4 ,x=(pi+4pin)/4

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Popular >

2sin(6x)+2sin(2x)=0

Solution

2 sin (6 x) + 2 sin (2 x) = 0

Solution

x = πn, x = \frac{π + 2 πn}{2}, x = \frac{3 π + 4 πn}{4}, x = \frac{π + 4 πn}{4}

Degrees

x = 0^{\circ} + 18 0^{\circ} n, x = 9 0^{\circ} + 18 0^{\circ} n, x = 13 5^{\circ} + 18 0^{\circ} n, x = 4 5^{\circ} + 18 0^{\circ} n

Solution steps

2 sin (6 x) + 2 sin (2 x) = 0

Let:

u = 2 x

2 sin (3 u) + 2 sin (u) = 0

Rewrite using trig identities

2 sin (3 u) + 2 sin (u)

sin (3 u) = 3 sin (u) - 4 sin^{3} (u)

sin (3 u)

Rewrite using trig identities

sin (3 u)

Rewrite as

= sin (2 u + u)

Use the Angle Sum identity:

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

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

Use the Double Angle identity:

sin (2 u) = 2 sin (u) cos (u)

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

Simplify

cos (2 u) sin (u) + cos (u) \cdot 2 sin (u) cos (u) : sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

cos (2 u) sin (u) + cos (u) 2 sin (u) cos (u)

cos (u) \cdot 2 sin (u) cos (u) = 2 cos^{2} (u) sin (u)

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

Apply exponent rule:

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

cos (u) cos (u) = cos^{1 + 1} (u)

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

Add the numbers:

1 + 1 = 2

= 2 sin (u) cos^{2} (u)

= sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

= sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

= sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

Use the Double Angle identity:

cos (2 u) = 1 - 2 sin^{2} (u)

= (1 - 2 sin^{2} (u)) sin (u) + 2 cos^{2} (u) sin (u)

Use the Pythagorean identity:

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

cos^{2} (u) = 1 - sin^{2} (u)

= (1 - 2 sin^{2} (u)) sin (u) + 2 (1 - sin^{2} (u)) sin (u)

Expand

(1 - 2 sin^{2} (u)) sin (u) + 2 (1 - sin^{2} (u)) sin (u) : - 4 sin^{3} (u) + 3 sin (u)

(1 - 2 sin^{2} (u)) sin (u) + 2 (1 - sin^{2} (u)) sin (u)

= sin (u) (1 - 2 sin^{2} (u)) + 2 sin (u) (1 - sin^{2} (u))

Expand

sin (u) (1 - 2 sin^{2} (u)) : sin (u) - 2 sin^{3} (u)

sin (u) (1 - 2 sin^{2} (u))

Apply the distributive law:

a (b - c) = ab - a c

a = sin (u), b = 1, c = 2 sin^{2} (u)

= sin (u) 1 - sin (u) 2 sin^{2} (u)

= 1 sin (u) - 2 sin^{2} (u) sin (u)

Simplify

1 \cdot sin (u) - 2 sin^{2} (u) sin (u) : sin (u) - 2 sin^{3} (u)

1 sin (u) - 2 sin^{2} (u) sin (u)

1 \cdot sin (u) = sin (u)

1 sin (u)

Multiply:

1 \cdot sin (u) = sin (u)

= sin (u)

2 sin^{2} (u) sin (u) = 2 sin^{3} (u)

2 sin^{2} (u) sin (u)

Apply exponent rule:

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

sin^{2} (u) sin (u) = sin^{2 + 1} (u)

= 2 sin^{2 + 1} (u)

Add the numbers:

2 + 1 = 3

= 2 sin^{3} (u)

= sin (u) - 2 sin^{3} (u)

= sin (u) - 2 sin^{3} (u)

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

Expand

2 sin (u) (1 - sin^{2} (u)) : 2 sin (u) - 2 sin^{3} (u)

2 sin (u) (1 - sin^{2} (u))

Apply the distributive law:

a (b - c) = ab - a c

a = 2 sin (u), b = 1, c = sin^{2} (u)

= 2 sin (u) 1 - 2 sin (u) sin^{2} (u)

= 2 \cdot 1 sin (u) - 2 sin^{2} (u) sin (u)

Simplify

2 \cdot 1 \cdot sin (u) - 2 sin^{2} (u) sin (u) : 2 sin (u) - 2 sin^{3} (u)

2 \cdot 1 sin (u) - 2 sin^{2} (u) sin (u)

2 \cdot 1 \cdot sin (u) = 2 sin (u)

2 \cdot 1 sin (u)

Multiply the numbers:

2 \cdot 1 = 2

= 2 sin (u)

2 sin^{2} (u) sin (u) = 2 sin^{3} (u)

2 sin^{2} (u) sin (u)

Apply exponent rule:

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

sin^{2} (u) sin (u) = sin^{2 + 1} (u)

= 2 sin^{2 + 1} (u)

Add the numbers:

2 + 1 = 3

= 2 sin^{3} (u)

= 2 sin (u) - 2 sin^{3} (u)

= 2 sin (u) - 2 sin^{3} (u)

= sin (u) - 2 sin^{3} (u) + 2 sin (u) - 2 sin^{3} (u)

Simplify

sin (u) - 2 sin^{3} (u) + 2 sin (u) - 2 sin^{3} (u) : - 4 sin^{3} (u) + 3 sin (u)

sin (u) - 2 sin^{3} (u) + 2 sin (u) - 2 sin^{3} (u)

Group like terms

= - 2 sin^{3} (u) - 2 sin^{3} (u) + sin (u) + 2 sin (u)

Add similar elements:

- 2 sin^{3} (u) - 2 sin^{3} (u) = - 4 sin^{3} (u)

= - 4 sin^{3} (u) + sin (u) + 2 sin (u)

Add similar elements:

sin (u) + 2 sin (u) = 3 sin (u)

= - 4 sin^{3} (u) + 3 sin (u)

= - 4 sin^{3} (u) + 3 sin (u)

= - 4 sin^{3} (u) + 3 sin (u)

= 2 (3 sin (u) - 4 sin^{3} (u)) + 2 sin (u)

Simplify

2 (3 sin (u) - 4 sin^{3} (u)) + 2 sin (u) : 8 sin (u) - 8 sin^{3} (u)

2 (3 sin (u) - 4 sin^{3} (u)) + 2 sin (u)

Expand

2 (3 sin (u) - 4 sin^{3} (u)) : 6 sin (u) - 8 sin^{3} (u)

2 (3 sin (u) - 4 sin^{3} (u))

Apply the distributive law:

a (b - c) = ab - a c

a = 2, b = 3 sin (u), c = 4 sin^{3} (u)

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

Simplify

2 \cdot 3 sin (u) - 2 \cdot 4 sin^{3} (u) : 6 sin (u) - 8 sin^{3} (u)

2 \cdot 3 sin (u) - 2 \cdot 4 sin^{3} (u)

Multiply the numbers:

2 \cdot 3 = 6

= 6 sin (u) - 2 \cdot 4 sin^{3} (u)

Multiply the numbers:

2 \cdot 4 = 8

= 6 sin (u) - 8 sin^{3} (u)

= 6 sin (u) - 8 sin^{3} (u)

= 6 sin (u) - 8 sin^{3} (u) + 2 sin (u)

Add similar elements:

6 sin (u) + 2 sin (u) = 8 sin (u)

= 8 sin (u) - 8 sin^{3} (u)

= 8 sin (u) - 8 sin^{3} (u)

8 sin (u) - 8 sin^{3} (u) = 0

Solve by substitution

8 sin (u) - 8 sin^{3} (u) = 0

Let:

sin (u) = u

8 u - 8 u^{3} = 0

8 u - 8 u^{3} = 0 : u = 0, u = - 1, u = 1

8 u - 8 u^{3} = 0

Factor

8 u - 8 u^{3} : - 8 u (u + 1) (u - 1)

8 u - 8 u^{3}

Factor out common term

- 8 u : - 8 u (u^{2} - 1)

- 8 u^{3} + 8 u

Apply exponent rule:

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

u^{3} = u^{2} u

= - 8 u^{2} u + 8 u

Factor out common term

- 8 u

= - 8 u (u^{2} - 1)

= - 8 u (u^{2} - 1)

Factor

u^{2} - 1 : (u + 1) (u - 1)

u^{2} - 1

Rewrite

1

1^{2}

= u^{2} - 1^{2}

Apply Difference of Two Squares Formula:

x^{2} - y^{2} = (x + y) (x - y)

u^{2} - 1^{2} = (u + 1) (u - 1)

= (u + 1) (u - 1)

= - 8 u (u + 1) (u - 1)

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

Using the Zero Factor Principle:

ab = 0

then

a = 0

b = 0

u = 0 or u + 1 = 0 or u - 1 = 0

Solve

u + 1 = 0 : u = - 1

u + 1 = 0

Move

1

to the right side

u + 1 = 0

Subtract

1

from both sides

u + 1 - 1 = 0 - 1

Simplify

u = - 1

u = - 1

Solve

u - 1 = 0 : u = 1

u - 1 = 0

Move

1

to the right side

u - 1 = 0

Add

1

to both sides

u - 1 + 1 = 0 + 1

Simplify

u = 1

u = 1

The solutions are

u = 0, u = - 1, u = 1

Substitute back

u = sin (u)

sin (u) = 0, sin (u) = - 1, sin (u) = 1

sin (u) = 0, sin (u) = - 1, sin (u) = 1

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

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

sin (u) = - 1

General solutions for

sin (u) = - 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}

u = \frac{3 π}{2} + 2 πn

u = \frac{3 π}{2} + 2 πn

sin (u) = 1 : u = \frac{π}{2} + 2 πn

sin (u) = 1

General solutions for

sin (u) = 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}

u = \frac{π}{2} + 2 πn

u = \frac{π}{2} + 2 πn

Combine all the solutions

u = 2 πn, u = π + 2 πn, u = \frac{3 π}{2} + 2 πn, u = \frac{π}{2} + 2 πn

Substitute back

u = 2 x

2 x = 2 πn : x = πn

2 x = 2 πn

Divide both sides by

2

2 x = 2 πn

Divide both sides by

2

\frac{2 x}{2} = \frac{2 πn}{2}

Simplify

x = πn

x = πn

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

2 x = π + 2 πn

Divide both sides by

2

2 x = π + 2 πn

Divide both sides by

2

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

Simplify

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

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

\frac{π}{2} + \frac{2 πn}{2} : \frac{π + 2 πn}{2}

\frac{π}{2} + \frac{2 πn}{2}

Apply rule

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

= \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

2 x = \frac{3 π}{2} + 2 πn : x = \frac{3 π + 4 πn}{4}

2 x = \frac{3 π}{2} + 2 πn

Divide both sides by

2

2 x = \frac{3 π}{2} + 2 πn

Divide both sides by

2

\frac{2 x}{2} = \frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2}

Simplify

\frac{2 x}{2} = \frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2}

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

\frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2} : \frac{3 π + 4 πn}{4}

\frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2}

Apply rule

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

= \frac{\frac{3 π}{2} + 2 πn}{2}

Join

\frac{3 π}{2} + 2 πn : \frac{3 π + 4 πn}{2}

\frac{3 π}{2} + 2 πn

Convert element to fraction:

2 πn = \frac{2 πn 2}{2}

= \frac{3 π}{2} + \frac{2 πn \cdot 2}{2}

Since the denominators are equal, combine the fractions:

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

= \frac{3 π + 2 πn \cdot 2}{2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{3 π + 4 πn}{2}

= \frac{\frac{3 π + 4 πn}{2}}{2}

Apply the fraction rule:

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

= \frac{3 π + 4 πn}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

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

2 x = \frac{π}{2} + 2 πn

Divide both sides by

2

2 x = \frac{π}{2} + 2 πn

Divide both sides by

2

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

Simplify

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

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

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

\frac{\frac{π}{2}}{2} + \frac{2 πn}{2}

Apply rule

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

= \frac{\frac{π}{2} + 2 πn}{2}

Join

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

\frac{π}{2} + 2 πn

Convert element to fraction:

2 πn = \frac{2 πn 2}{2}

= \frac{π}{2} + \frac{2 πn \cdot 2}{2}

Since the denominators are equal, combine the fractions:

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

= \frac{π + 2 πn \cdot 2}{2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{π + 4 πn}{2}

= \frac{\frac{π + 4 πn}{2}}{2}

Apply the fraction rule:

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

= \frac{π + 4 πn}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = πn, x = \frac{π + 2 πn}{2}, x = \frac{3 π + 4 πn}{4}, x = \frac{π + 4 πn}{4}

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Frequently Asked Questions (FAQ)

What is the general solution for 2sin(6x)+2sin(2x)=0 ?
The general solution for 2sin(6x)+2sin(2x)=0 is x=pin,x=(pi+2pin)/2 ,x=(3pi+4pin)/4 ,x=(pi+4pin)/4