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Popular Trigonometry >

2sin^2(x)-sqrt(2sin(x))=0

Solution

2 sin^{2} (x) - 2 sin (x) = 0

Solution

x = 2 πn, x = π + 2 πn, x = 0.91686 \dots + 2 πn, x = π - 0.91686 \dots + 2 πn

Degrees

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = 52.53268 \dots^{\circ} + 36 0^{\circ} n, x = 127.46731 \dots^{\circ} + 36 0^{\circ} n

Solution steps

2 sin^{2} (x) - 2 sin (x) = 0

Solve by substitution

2 sin^{2} (x) - 2 sin (x) = 0

Let:

sin (x) = u

2 u^{2} - 2 u = 0

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

2 u^{2} - 2 u = 0

Remove square roots

2 u^{2} - 2 u = 0

Subtract

2 u^{2}

from both sides

2 u^{2} - 2 u - 2 u^{2} = 0 - 2 u^{2}

Simplify

- 2 u = - 2 u^{2}

Square both sides:

2 u = 4 u^{4}

2 u^{2} - 2 u = 0

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

Expand

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

(- 2 u)^{2}

Apply exponent rule:

(- a)^{n} = a^{n},

n

is even

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

= (2 u)^{2}

Apply radical rule:

a = a^{\frac{1}{2}}

= ((2 u)^{\frac{1}{2}})^{2}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= (2 u)^{\frac{1}{2} \cdot 2}

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

\frac{1}{2} \cdot 2

Multiply fractions:

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

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

Cancel the common factor:

2

= 1

= 2 u

Expand

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

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

Apply exponent rule:

(- a)^{n} = a^{n},

n

is even

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

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

Apply exponent rule:

(a \cdot b)^{n} = a^{n} b^{n}

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

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

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= u^{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= u^{4}

= 2^{2} u^{4}

2^{2} = 4

= 4 u^{4}

2 u = 4 u^{4}

2 u = 4 u^{4}

2 u = 4 u^{4}

Solve

2 u = 4 u^{4} : u = 0, u = \frac{2 ^{\frac{2}{3}}}{2}

2 u = 4 u^{4}

Move

4 u^{4}

to the left side

2 u = 4 u^{4}

Subtract

4 u^{4}

from both sides

2 u - 4 u^{4} = 4 u^{4} - 4 u^{4}

Simplify

2 u - 4 u^{4} = 0

2 u - 4 u^{4} = 0

Factor

2 u - 4 u^{4}

Factor out common term

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

- 4 u^{4} + 2 u

Apply exponent rule:

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

u^{4} = u^{3} u

= - 4 u^{3} u + 2 u

Rewrite

4

2 \cdot 2

= - 2 \cdot 2 u^{3} u + 2 u

Factor out common term

- 2 u

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

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

Factor

2 u^{3} - 1

Rewrite

2 u^{3} - 1

2 u^{3} - 1

Apply radical rule:

a = (a)^{2}

Rewrite

1

1^{3}

Apply exponent rule:

a^{m} b^{m} = (ab)^{m}

Apply Difference of Cubes Formula:

x^{3} - y^{3} = (x - y) (x^{2} + x y + y^{2})

Refine

Using the Zero Factor Principle:

ab = 0

then

a = 0

b = 0

Solve

Move

1

to the right side

Add

1

to both sides

Simplify

Divide both sides by

Simplify

Cancel the common factor:

= u

Simplify

Multiply by the conjugate

\frac{2 ^{\frac{2}{3}}}{2 ^{\frac{2}{3}}}

1 \cdot 2^{\frac{2}{3}} = 2^{\frac{2}{3}}

Apply exponent rule:

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

= 2^{\frac{2}{3} + \frac{1}{3}}

Join

\frac{2}{3} + \frac{1}{3} : 1

\frac{2}{3} + \frac{1}{3}

Since the denominators are equal, combine the fractions:

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

= \frac{2 + 1}{3}

Add the numbers:

2 + 1 = 3

= \frac{3}{3}

Apply rule

\frac{a}{a} = 1

= 1

= 2^{1}

Apply rule

a^{1} = a

= 2

= \frac{2 ^{\frac{2}{3}}}{2}

u = \frac{2 ^{\frac{2}{3}}}{2}

u = \frac{2 ^{\frac{2}{3}}}{2}

u = \frac{2 ^{\frac{2}{3}}}{2}

Solve

No Solution for

u \in R

Discriminant

For a quadratic equation of the form

a x^{2} + b x + c = 0

the discriminant is

b^{2} - 4 a c

For

Expand

Apply radical rule:

= (2^{\frac{1}{3}})^{2}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= 2^{\frac{1}{3} \cdot 2}

\frac{1}{3} \cdot 2 = \frac{2}{3}

\frac{1}{3} \cdot 2

Multiply fractions:

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

= \frac{1 \cdot 2}{3}

Multiply the numbers:

1 \cdot 2 = 2

= \frac{2}{3}

= 2^{\frac{2}{3}}

4 \cdot 2^{\frac{2}{3}} \cdot 1 = 4 \cdot 2^{\frac{2}{3}}

4 \cdot 2^{\frac{2}{3}} \cdot 1

Multiply the numbers:

4 \cdot 1 = 4

= 4 \cdot 2^{\frac{2}{3}}

= 2^{\frac{2}{3}} - 4 \cdot 2^{\frac{2}{3}}

Add similar elements:

2^{\frac{2}{3}} - 4 \cdot 2^{\frac{2}{3}} = - 3 \cdot 2^{\frac{2}{3}}

= - 3 \cdot 2^{\frac{2}{3}}

- 3 \cdot 2^{\frac{2}{3}}

Discriminant cannot be negative for

u \in R

The solution is

No Solution for u \in R

The solutions are

u = 0, u = \frac{2 ^{\frac{2}{3}}}{2}

u = 0, u = \frac{2 ^{\frac{2}{3}}}{2}

Verify Solutions:

u = 0

True

, u = \frac{2 ^{\frac{2}{3}}}{2}

True

Check the solutions by plugging them into

2 u^{2} - 2 u = 0

Remove the ones that don't agree with the equation.

Plug in

u = 0 :

True

2 \cdot 0^{2} - 2 \cdot 0 = 0

2 \cdot 0^{2} - 2 \cdot 0 = 0

2 \cdot 0^{2} - 2 \cdot 0

Apply rule

0^{a} = 0

0^{2} = 0

= 2 \cdot 0 - 2 \cdot 0

2 \cdot 0 = 0

2 \cdot 0

Apply rule

0 \cdot a = 0

= 0

2 \cdot 0 = 0

2 \cdot 0

Apply rule

0 \cdot a = 0

= 0

Apply rule

0 = 0

= 0

= 0 - 0

Subtract the numbers:

0 - 0 = 0

= 0

0 = 0

True

Plug in

u = \frac{2 ^{\frac{2}{3}}}{2} :

True

2 (\frac{2 ^{\frac{2}{3}}}{2})^{2} - 2 (\frac{2 ^{\frac{2}{3}}}{2}) = 0

2 (\frac{2 ^{\frac{2}{3}}}{2})^{2} - 2 (\frac{2 ^{\frac{2}{3}}}{2}) = 2^{\frac{1}{3}} - 2^{\frac{2}{3}}

2 (\frac{2 ^{\frac{2}{3}}}{2})^{2} - 2 (\frac{2 ^{\frac{2}{3}}}{2})

Remove parentheses:

(a) = a

= 2 (\frac{2 ^{\frac{2}{3}}}{2})^{2} - 2 \cdot \frac{2 ^{\frac{2}{3}}}{2}

2 (\frac{2 ^{\frac{2}{3}}}{2})^{2} = 2^{\frac{1}{3}}

2 (\frac{2 ^{\frac{2}{3}}}{2})^{2}

(\frac{2 ^{\frac{2}{3}}}{2})^{2} = \frac{1}{2 ^{\frac{2}{3}}}

(\frac{2 ^{\frac{2}{3}}}{2})^{2}

\frac{2 ^{\frac{2}{3}}}{2} = \frac{1}{2 ^{\frac{1}{3}}}

\frac{2 ^{\frac{2}{3}}}{2}

Apply exponent rule:

\frac{x ^{a}}{x ^{b}} = \frac{1}{x ^{b - a}}

\frac{2 ^{\frac{2}{3}}}{2} = \frac{1}{2 ^{1 - \frac{2}{3}}}

= \frac{1}{2 ^{1 - \frac{2}{3}}}

Subtract the numbers:

1 - \frac{2}{3} = \frac{1}{3}

= \frac{1}{2 ^{\frac{1}{3}}}

= (\frac{1}{2 ^{\frac{1}{3}}})^{2}

Apply exponent rule:

(\frac{a}{b})^{c} = \frac{a ^{c}}{b ^{c}}

= \frac{1 ^{2}}{( 2 ^{\frac{1}{3}} ) ^{2}}

(2^{\frac{1}{3}})^{2} : 2^{\frac{2}{3}}

Apply exponent rule:

(a^{b})^{c} = a^{b c}

= 2^{\frac{1}{3} \cdot 2}

\frac{1}{3} \cdot 2 = \frac{2}{3}

\frac{1}{3} \cdot 2

Multiply fractions:

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

= \frac{1 \cdot 2}{3}

Multiply the numbers:

1 \cdot 2 = 2

= \frac{2}{3}

= 2^{\frac{2}{3}}

= \frac{1 ^{2}}{2 ^{\frac{2}{3}}}

Apply rule

1^{a} = 1

1^{2} = 1

= \frac{1}{2 ^{\frac{2}{3}}}

= 2 \cdot \frac{1}{2 ^{\frac{2}{3}}}

Multiply fractions:

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

= \frac{1 \cdot 2}{2 ^{\frac{2}{3}}}

Multiply the numbers:

1 \cdot 2 = 2

= \frac{2}{2 ^{\frac{2}{3}}}

Apply exponent rule:

\frac{x ^{a}}{x ^{b}} = x^{a - b}

\frac{2}{2 ^{\frac{2}{3}}} = 2^{1 - \frac{2}{3}}

= 2^{1 - \frac{2}{3}}

Subtract the numbers:

1 - \frac{2}{3} = \frac{1}{3}

= 2^{\frac{1}{3}}

2 \cdot \frac{2 ^{\frac{2}{3}}}{2} = 2^{\frac{2}{3}}

2 \cdot \frac{2 ^{\frac{2}{3}}}{2}

Multiply

2 \cdot \frac{2 ^{\frac{2}{3}}}{2} : 2^{\frac{2}{3}}

2 \cdot \frac{2 ^{\frac{2}{3}}}{2}

Multiply fractions:

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

= \frac{2 ^{\frac{2}{3}} \cdot 2}{2}

Cancel the common factor:

2

= 2^{\frac{2}{3}}

= 2^{\frac{2}{3}}

= 2^{\frac{1}{3}} - 2^{\frac{2}{3}}

2^{\frac{1}{3}} - 2^{\frac{2}{3}} = 0

True

The solutions are

u = 0, u = \frac{2 ^{\frac{2}{3}}}{2}

Substitute back

u = sin (x)

sin (x) = 0, sin (x) = \frac{2 ^{\frac{2}{3}}}{2}

sin (x) = 0, sin (x) = \frac{2 ^{\frac{2}{3}}}{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{2 ^{\frac{2}{3}}}{2} : x = arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn, x = π - arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn

sin (x) = \frac{2 ^{\frac{2}{3}}}{2}

Apply trig inverse properties

sin (x) = \frac{2 ^{\frac{2}{3}}}{2}

General solutions for

sin (x) = \frac{2 ^{\frac{2}{3}}}{2}

sin (x) = a \Rightarrow x = arcsin (a) + 2 πn, x = π - arcsin (a) + 2 πn

x = arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn, x = π - arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn

x = arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn, x = π - arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn

Combine all the solutions

x = 2 πn, x = π + 2 πn, x = arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn, x = π - arcsin (\frac{2 ^{\frac{2}{3}}}{2}) + 2 πn

Show solutions in decimal form

x = 2 πn, x = π + 2 πn, x = 0.91686 \dots + 2 πn, x = π - 0.91686 \dots + 2 πn

Graph

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