What is the general solution for sin^3(x)-4sin(x)=0 ?

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

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Popular >

sin^3(x)-4sin(x)=0

Solution

sin^{3} (x) - 4 sin (x) = 0

Solution

x = 2 πn, x = π + 2 πn

Degrees

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

Solution steps

sin^{3} (x) - 4 sin (x) = 0

Solve by substitution

sin^{3} (x) - 4 sin (x) = 0

Let:

sin (x) = u

u^{3} - 4 u = 0

u^{3} - 4 u = 0 : u = 0, u = - 2, u = 2

u^{3} - 4 u = 0

Factor

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

u^{3} - 4 u

Factor out common term

u : u (u^{2} - 4)

u^{3} - 4 u

Apply exponent rule:

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

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

= u^{2} u - 4 u

Factor out common term

u

= u (u^{2} - 4)

= u (u^{2} - 4)

Factor

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

u^{2} - 4

Rewrite

4

2^{2}

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

Apply Difference of Two Squares Formula:

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

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

= (u + 2) (u - 2)

= u (u + 2) (u - 2)

u (u + 2) (u - 2) = 0

Using the Zero Factor Principle:

ab = 0

then

a = 0

b = 0

u = 0 or u + 2 = 0 or u - 2 = 0

Solve

u + 2 = 0 : u = - 2

u + 2 = 0

Move

2

to the right side

u + 2 = 0

Subtract

2

from both sides

u + 2 - 2 = 0 - 2

Simplify

u = - 2

u = - 2

Solve

u - 2 = 0 : u = 2

u - 2 = 0

Move

2

to the right side

u - 2 = 0

Add

2

to both sides

u - 2 + 2 = 0 + 2

Simplify

u = 2

u = 2

The solutions are

u = 0, u = - 2, u = 2

Substitute back

u = sin (x)

sin (x) = 0, sin (x) = - 2, sin (x) = 2

sin (x) = 0, sin (x) = - 2, sin (x) = 2

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

sin (x) = - 2 :

No Solution

sin (x) = - 2

- 1 \leq sin (x) \leq 1

No Solution

sin (x) = 2 :

No Solution

sin (x) = 2

- 1 \leq sin (x) \leq 1

No Solution

Combine all the solutions

x = 2 πn, x = π + 2 πn

Popular Examples

cos(a)=(-82)/(sqrt(140)*\sqrt{138)}

cos (a) = \frac{- 82}{140 \cdot 138}

sec^2(x)-cos(x)=0

sec^{2} (x) - cos (x) = 0

sin(x)*sec(x)=0

sin (x) \cdot sec (x) = 0

cos(x)=-0.1235,0<= x<= 2pi

cos (x) = - 0.1235, 0 \leq x \leq 2 π

sin((3pi)/x)=0

sin (\frac{3 π}{x}) = 0

Frequently Asked Questions (FAQ)

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