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Popular Trigonometry >

sin^2(x)+2sin^2(x/2)=1

Solution

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

Solution

x = - 2 \cdot 0.45227 \dots + 4 πn, x = 2 π + 2 \cdot 0.45227 \dots + 4 πn, x = 2 \cdot 0.45227 \dots + 4 πn, x = 2 π - 2 \cdot 0.45227 \dots + 4 πn

Degrees

x = - 51.82729 \dots^{\circ} + 72 0^{\circ} n, x = 411.82729 \dots^{\circ} + 72 0^{\circ} n, x = 51.82729 \dots^{\circ} + 72 0^{\circ} n, x = 308.17270 \dots^{\circ} + 72 0^{\circ} n

Solution steps

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

Subtract

1

from both sides

sin^{2} (x) + 2 sin^{2} (\frac{x}{2}) - 1 = 0

Let:

u = \frac{x}{2}

sin^{2} (2 u) + 2 sin^{2} (u) - 1 = 0

Rewrite using trig identities

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

Use the Pythagorean identity:

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

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

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

- cos^{2} (2 u) + 2 sin^{2} (u) = 0

Factor

- cos^{2} (2 u) + 2 sin^{2} (u) : (2 sin (u) + cos (2 u)) (2 sin (u) - cos (2 u))

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

Rewrite

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

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

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

Apply radical rule:

a = (a)^{2}

2 = (2)^{2}

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

Apply exponent rule:

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

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

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

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

Apply Difference of Two Squares Formula:

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

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

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

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

Solving each part separately

2 sin (u) + cos (2 u) = 0 or 2 sin (u) - cos (2 u) = 0

2 sin (u) + cos (2 u) = 0 : u = arcsin (- \frac{- 2 + 10}{4}) + 2 πn, u = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

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

Rewrite using trig identities

cos (2 u) + sin (u) 2

Use the Double Angle identity:

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

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

1 - 2 sin^{2} (u) + sin (u) 2 = 0

Solve by substitution

1 - 2 sin^{2} (u) + sin (u) 2 = 0

Let:

sin (u) = u

1 - 2 u^{2} + u 2 = 0

1 - 2 u^{2} + u 2 = 0 : u = - \frac{- 2 + 10}{4}, u = \frac{2 + 10}{4}

1 - 2 u^{2} + u 2 = 0

Write in the standard form

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

- 2 u^{2} + 2 u + 1 = 0

Solve with the quadratic formula

- 2 u^{2} + 2 u + 1 = 0

Quadratic Equation Formula:

For

a = - 2, b = 2, c = 1

u_{1, 2} = \frac{- 2 \pm ( 2 ) ^{2} - 4 ( - 2 ) \cdot 1}{2 ( - 2 )}

u_{1, 2} = \frac{- 2 \pm ( 2 ) ^{2} - 4 ( - 2 ) \cdot 1}{2 ( - 2 )}

(2)^{2} - 4 (- 2) \cdot 1 = 10

(2)^{2} - 4 (- 2) \cdot 1

Apply rule

- (- a) = a

= (2)^{2} + 4 \cdot 2 \cdot 1

(2)^{2} = 2

(2)^{2}

Apply radical rule:

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

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

Apply exponent rule:

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

= 2^{\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

4 \cdot 2 \cdot 1 = 8

4 \cdot 2 \cdot 1

Multiply the numbers:

4 \cdot 2 \cdot 1 = 8

= 8

= 2 + 8

Add the numbers:

2 + 8 = 10

= 10

u_{1, 2} = \frac{- 2 \pm 10}{2 ( - 2 )}

Separate the solutions

u_{1} = \frac{- 2 + 10}{2 ( - 2 )}, u_{2} = \frac{- 2 - 10}{2 ( - 2 )}

u = \frac{- 2 + 10}{2 ( - 2 )} : - \frac{- 2 + 10}{4}

\frac{- 2 + 10}{2 ( - 2 )}

Remove parentheses:

(- a) = - a

= \frac{- 2 + 10}{- 2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{- 2 + 10}{- 4}

Apply the fraction rule:

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

= - \frac{- 2 + 10}{4}

u = \frac{- 2 - 10}{2 ( - 2 )} : \frac{2 + 10}{4}

\frac{- 2 - 10}{2 ( - 2 )}

Remove parentheses:

(- a) = - a

= \frac{- 2 - 10}{- 2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{- 2 - 10}{- 4}

Apply the fraction rule:

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

- 2 - 10 = - (2 + 10)

= \frac{2 + 10}{4}

The solutions to the quadratic equation are:

u = - \frac{- 2 + 10}{4}, u = \frac{2 + 10}{4}

Substitute back

u = sin (u)

sin (u) = - \frac{- 2 + 10}{4}, sin (u) = \frac{2 + 10}{4}

sin (u) = - \frac{- 2 + 10}{4}, sin (u) = \frac{2 + 10}{4}

sin (u) = - \frac{- 2 + 10}{4} : u = arcsin (- \frac{- 2 + 10}{4}) + 2 πn, u = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

sin (u) = - \frac{- 2 + 10}{4}

Apply trig inverse properties

sin (u) = - \frac{- 2 + 10}{4}

General solutions for

sin (u) = - \frac{- 2 + 10}{4}

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

u = arcsin (- \frac{- 2 + 10}{4}) + 2 πn, u = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

u = arcsin (- \frac{- 2 + 10}{4}) + 2 πn, u = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

sin (u) = \frac{2 + 10}{4} :

No Solution

sin (u) = \frac{2 + 10}{4}

- 1 \leq sin (x) \leq 1

No Solution

Combine all the solutions

u = arcsin (- \frac{- 2 + 10}{4}) + 2 πn, u = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

2 sin (u) - cos (2 u) = 0 : u = arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

2 sin (u) - cos (2 u) = 0

Rewrite using trig identities

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

Use the Double Angle identity:

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

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

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

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

Distribute parentheses

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

Apply minus-plus rules

- (- a) = a, - (a) = - a

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

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

- 1 + 2 sin^{2} (u) + sin (u) 2 = 0

Solve by substitution

- 1 + 2 sin^{2} (u) + sin (u) 2 = 0

Let:

sin (u) = u

- 1 + 2 u^{2} + u 2 = 0

- 1 + 2 u^{2} + u 2 = 0 : u = \frac{- 2 + 10}{4}, u = \frac{- 2 - 10}{4}

- 1 + 2 u^{2} + u 2 = 0

Write in the standard form

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

2 u^{2} + 2 u - 1 = 0

Solve with the quadratic formula

2 u^{2} + 2 u - 1 = 0

Quadratic Equation Formula:

For

a = 2, b = 2, c = - 1

u_{1, 2} = \frac{- 2 \pm ( 2 ) ^{2} - 4 \cdot 2 ( - 1 )}{2 \cdot 2}

u_{1, 2} = \frac{- 2 \pm ( 2 ) ^{2} - 4 \cdot 2 ( - 1 )}{2 \cdot 2}

(2)^{2} - 4 \cdot 2 (- 1) = 10

(2)^{2} - 4 \cdot 2 (- 1)

Apply rule

- (- a) = a

= (2)^{2} + 4 \cdot 2 \cdot 1

(2)^{2} = 2

(2)^{2}

Apply radical rule:

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

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

Apply exponent rule:

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

= 2^{\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

4 \cdot 2 \cdot 1 = 8

4 \cdot 2 \cdot 1

Multiply the numbers:

4 \cdot 2 \cdot 1 = 8

= 8

= 2 + 8

Add the numbers:

2 + 8 = 10

= 10

u_{1, 2} = \frac{- 2 \pm 10}{2 \cdot 2}

Separate the solutions

u_{1} = \frac{- 2 + 10}{2 \cdot 2}, u_{2} = \frac{- 2 - 10}{2 \cdot 2}

u = \frac{- 2 + 10}{2 \cdot 2} : \frac{- 2 + 10}{4}

\frac{- 2 + 10}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{- 2 + 10}{4}

u = \frac{- 2 - 10}{2 \cdot 2} : \frac{- 2 - 10}{4}

\frac{- 2 - 10}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{- 2 - 10}{4}

The solutions to the quadratic equation are:

u = \frac{- 2 + 10}{4}, u = \frac{- 2 - 10}{4}

Substitute back

u = sin (u)

sin (u) = \frac{- 2 + 10}{4}, sin (u) = \frac{- 2 - 10}{4}

sin (u) = \frac{- 2 + 10}{4}, sin (u) = \frac{- 2 - 10}{4}

sin (u) = \frac{- 2 + 10}{4} : u = arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

sin (u) = \frac{- 2 + 10}{4}

Apply trig inverse properties

sin (u) = \frac{- 2 + 10}{4}

General solutions for

sin (u) = \frac{- 2 + 10}{4}

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

u = arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

u = arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

sin (u) = \frac{- 2 - 10}{4} :

No Solution

sin (u) = \frac{- 2 - 10}{4}

- 1 \leq sin (x) \leq 1

No Solution

Combine all the solutions

u = arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

Combine all the solutions

u = arcsin (- \frac{- 2 + 10}{4}) + 2 πn, u = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = arcsin (\frac{- 2 + 10}{4}) + 2 πn, u = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

Substitute back

u = \frac{x}{2}

\frac{x}{2} = arcsin (- \frac{- 2 + 10}{4}) + 2 πn : x = - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

\frac{x}{2} = arcsin (- \frac{- 2 + 10}{4}) + 2 πn

Simplify

arcsin (- \frac{- 2 + 10}{4}) + 2 πn : - arcsin (\frac{10 - 2}{4}) + 2 πn

arcsin (- \frac{- 2 + 10}{4}) + 2 πn

Use the following property:

arcsin (- x) = - arcsin (x)

arcsin (- \frac{10 - 2}{4}) = - arcsin (\frac{10 - 2}{4})

= - arcsin (\frac{10 - 2}{4}) + 2 πn

\frac{x}{2} = - arcsin (\frac{10 - 2}{4}) + 2 πn

Multiply both sides by

2

\frac{x}{2} = - arcsin (\frac{10 - 2}{4}) + 2 πn

Multiply both sides by

2

\frac{2 x}{2} = - 2 arcsin (\frac{10 - 2}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} = - 2 arcsin (\frac{10 - 2}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

- 2 arcsin (\frac{10 - 2}{4}) + 2 \cdot 2 πn : - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

- 2 arcsin (\frac{10 - 2}{4}) + 2 \cdot 2 πn

Multiply the numbers:

2 \cdot 2 = 4

= - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

x = - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

x = - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

x = - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

\frac{x}{2} = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn : x = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

\frac{x}{2} = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

Multiply both sides by

2

\frac{x}{2} = π + arcsin (\frac{- 2 + 10}{4}) + 2 πn

Multiply both sides by

2

\frac{2 x}{2} = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn : 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Multiply the numbers:

2 \cdot 2 = 4

= 2 π + 2 arcsin (\frac{10 - 2}{4}) + 4 πn

x = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

\frac{x}{2} = arcsin (\frac{- 2 + 10}{4}) + 2 πn : x = 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

\frac{x}{2} = arcsin (\frac{- 2 + 10}{4}) + 2 πn

Multiply both sides by

2

\frac{x}{2} = arcsin (\frac{- 2 + 10}{4}) + 2 πn

Multiply both sides by

2

\frac{2 x}{2} = 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} = 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn : 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Multiply the numbers:

2 \cdot 2 = 4

= 2 arcsin (\frac{10 - 2}{4}) + 4 πn

x = 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

\frac{x}{2} = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn : x = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

\frac{x}{2} = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

Multiply both sides by

2

\frac{x}{2} = π - arcsin (\frac{- 2 + 10}{4}) + 2 πn

Multiply both sides by

2

\frac{2 x}{2} = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn : 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 2 \cdot 2 πn

Multiply the numbers:

2 \cdot 2 = 4

= 2 π - 2 arcsin (\frac{10 - 2}{4}) + 4 πn

x = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

x = - 2 arcsin (\frac{10 - 2}{4}) + 4 πn, x = 2 π + 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn, x = 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn, x = 2 π - 2 arcsin (\frac{- 2 + 10}{4}) + 4 πn

Show solutions in decimal form

x = - 2 \cdot 0.45227 \dots + 4 πn, x = 2 π + 2 \cdot 0.45227 \dots + 4 πn, x = 2 \cdot 0.45227 \dots + 4 πn, x = 2 π - 2 \cdot 0.45227 \dots + 4 πn

Graph

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