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Popular Trigonometry >

2sin^3(x)-5sin^2(x)+2sin(x)=0

Solution

2 sin^{3} (x) - 5 sin^{2} (x) + 2 sin (x) = 0

Solution

x = 2 πn, x = π + 2 πn, x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

Degrees

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = 3 0^{\circ} + 36 0^{\circ} n, x = 15 0^{\circ} + 36 0^{\circ} n

Solution steps

2 sin^{3} (x) - 5 sin^{2} (x) + 2 sin (x) = 0

Solve by substitution

2 sin^{3} (x) - 5 sin^{2} (x) + 2 sin (x) = 0

Let:

sin (x) = u

2 u^{3} - 5 u^{2} + 2 u = 0

2 u^{3} - 5 u^{2} + 2 u = 0 : u = 0, u = \frac{1}{2}, u = 2

2 u^{3} - 5 u^{2} + 2 u = 0

Factor

2 u^{3} - 5 u^{2} + 2 u : u (2 u - 1) (u - 2)

2 u^{3} - 5 u^{2} + 2 u

Factor out common term

u : u (2 u^{2} - 5 u + 2)

2 u^{3} - 5 u^{2} + 2 u

Apply exponent rule:

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

u^{2} = uu

= 2 u^{2} u - 5 uu + 2 u

Factor out common term

u

= u (2 u^{2} - 5 u + 2)

= u (2 u^{2} - 5 u + 2)

Factor

2 u^{2} - 5 u + 2 : (2 u - 1) (u - 2)

2 u^{2} - 5 u + 2

Break the expression into groups

2 u^{2} - 5 u + 2

Definition

Factors of

4 : 1, 2, 4

4

Divisors (Factors)

Find the Prime factors of

4 : 2, 2

4

4

divides by

24 = 2 \cdot 2

= 2 \cdot 2

2

is a prime number, therefore no further factorization is possible

= 2 \cdot 2

Add the prime factors:

2

Add 1 and the number

4

itself

1, 4

The factors of

4

1, 2, 4

Negative factors of

4 : - 1, - 2, - 4

Multiply the factors by

- 1

to get the negative factors

- 1, - 2, - 4

For every two factors such that

u * v = 4,

check if

u + v = - 5

Check

u = 1, v = 4 : u * v = 4, u + v = 5 \Rightarrow

FalseCheck

u = 2, v = 2 : u * v = 4, u + v = 4 \Rightarrow

False

u = - 1, v = - 4

Group into

(a x^{2} + ux) + (vx + c)

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

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

Factor out

u

from

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

2 u^{2} - u

Apply exponent rule:

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

u^{2} = uu

= 2 uu - u

Factor out common term

u

= u (2 u - 1)

Factor out

- 2

from

- 4 u + 2 : - 2 (2 u - 1)

- 4 u + 2

Rewrite

4

2 \cdot 2

= - 2 \cdot 2 u + 2

Factor out common term

- 2

= - 2 (2 u - 1)

= u (2 u - 1) - 2 (2 u - 1)

Factor out common term

2 u - 1

= (2 u - 1) (u - 2)

= u (2 u - 1) (u - 2)

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

Using the Zero Factor Principle:

ab = 0

then

a = 0

b = 0

u = 0 or 2 u - 1 = 0 or u - 2 = 0

Solve

2 u - 1 = 0 : u = \frac{1}{2}

2 u - 1 = 0

Move

1

to the right side

2 u - 1 = 0

Add

1

to both sides

2 u - 1 + 1 = 0 + 1

Simplify

2 u = 1

2 u = 1

Divide both sides by

2

2 u = 1

Divide both sides by

2

\frac{2 u}{2} = \frac{1}{2}

Simplify

u = \frac{1}{2}

u = \frac{1}{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 = \frac{1}{2}, u = 2

Substitute back

u = sin (x)

sin (x) = 0, sin (x) = \frac{1}{2}, sin (x) = 2

sin (x) = 0, sin (x) = \frac{1}{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) = \frac{1}{2} : x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

sin (x) = \frac{1}{2}

General solutions for

sin (x) = \frac{1}{2}

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 = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

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, x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

Graph

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