What is the general solution for sin^2(θ)=5(cos(θ)+1) ?

The general solution for sin^2(θ)=5(cos(θ)+1) is θ=pi+2pin

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sin^2(θ)=5(cos(θ)+1)

Solution

sin^{2} (θ) = 5 (cos (θ) + 1)

Solution

θ = π + 2 πn

Degrees

θ = 18 0^{\circ} + 36 0^{\circ} n

Solution steps

sin^{2} (θ) = 5 (cos (θ) + 1)

Subtract

5 (cos (θ) + 1)

from both sides

sin^{2} (θ) - 5 (cos (θ) + 1) = 0

Rewrite using trig identities

sin^{2} (θ) - (1 + cos (θ)) \cdot 5

Use the Pythagorean identity:

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

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

= 1 - cos^{2} (θ) - (1 + cos (θ)) \cdot 5

Simplify

1 - cos^{2} (θ) - (1 + cos (θ)) \cdot 5 : - cos^{2} (θ) - 5 cos (θ) - 4

1 - cos^{2} (θ) - (1 + cos (θ)) \cdot 5

= 1 - cos^{2} (θ) - 5 (1 + cos (θ))

Expand

- 5 (1 + cos (θ)) : - 5 - 5 cos (θ)

- 5 (1 + cos (θ))

Apply the distributive law:

a (b + c) = ab + a c

a = - 5, b = 1, c = cos (θ)

= - 5 \cdot 1 + (- 5) cos (θ)

Apply minus-plus rules

+ (- a) = - a

= - 5 \cdot 1 - 5 cos (θ)

Multiply the numbers:

5 \cdot 1 = 5

= - 5 - 5 cos (θ)

= 1 - cos^{2} (θ) - 5 - 5 cos (θ)

Simplify

1 - cos^{2} (θ) - 5 - 5 cos (θ) : - cos^{2} (θ) - 5 cos (θ) - 4

1 - cos^{2} (θ) - 5 - 5 cos (θ)

Group like terms

= - cos^{2} (θ) - 5 cos (θ) + 1 - 5

Add/Subtract the numbers:

1 - 5 = - 4

= - cos^{2} (θ) - 5 cos (θ) - 4

= - cos^{2} (θ) - 5 cos (θ) - 4

= - cos^{2} (θ) - 5 cos (θ) - 4

- 4 - cos^{2} (θ) - 5 cos (θ) = 0

Solve by substitution

- 4 - cos^{2} (θ) - 5 cos (θ) = 0

Let:

cos (θ) = u

- 4 - u^{2} - 5 u = 0

- 4 - u^{2} - 5 u = 0 : u = - 4, u = - 1

- 4 - u^{2} - 5 u = 0

Write in the standard form

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

- u^{2} - 5 u - 4 = 0

Solve with the quadratic formula

- u^{2} - 5 u - 4 = 0

Quadratic Equation Formula:

For

a = - 1, b = - 5, c = - 4

u_{1, 2} = \frac{- ( - 5 ) \pm ( - 5 ) ^{2} - 4 ( - 1 ) ( - 4 )}{2 ( - 1 )}

u_{1, 2} = \frac{- ( - 5 ) \pm ( - 5 ) ^{2} - 4 ( - 1 ) ( - 4 )}{2 ( - 1 )}

(- 5)^{2} - 4 (- 1) (- 4) = 3

(- 5)^{2} - 4 (- 1) (- 4)

Apply rule

- (- a) = a

= (- 5)^{2} - 4 \cdot 1 \cdot 4

Apply exponent rule:

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

n

is even

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

= 5^{2} - 4 \cdot 1 \cdot 4

Multiply the numbers:

4 \cdot 1 \cdot 4 = 16

= 5^{2} - 16

5^{2} = 25

= 25 - 16

Subtract the numbers:

25 - 16 = 9

= 9

Factor the number:

9 = 3^{2}

= 3^{2}

Apply radical rule:

3^{2} = 3

= 3

u_{1, 2} = \frac{- ( - 5 ) \pm 3}{2 ( - 1 )}

Separate the solutions

u_{1} = \frac{- ( - 5 ) + 3}{2 ( - 1 )}, u_{2} = \frac{- ( - 5 ) - 3}{2 ( - 1 )}

u = \frac{- ( - 5 ) + 3}{2 ( - 1 )} : - 4

\frac{- ( - 5 ) + 3}{2 ( - 1 )}

Remove parentheses:

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

= \frac{5 + 3}{- 2 \cdot 1}

Add the numbers:

5 + 3 = 8

= \frac{8}{- 2 \cdot 1}

Multiply the numbers:

2 \cdot 1 = 2

= \frac{8}{- 2}

Apply the fraction rule:

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

= - \frac{8}{2}

Divide the numbers:

\frac{8}{2} = 4

= - 4

u = \frac{- ( - 5 ) - 3}{2 ( - 1 )} : - 1

\frac{- ( - 5 ) - 3}{2 ( - 1 )}

Remove parentheses:

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

= \frac{5 - 3}{- 2 \cdot 1}

Subtract the numbers:

5 - 3 = 2

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

Multiply the numbers:

2 \cdot 1 = 2

= \frac{2}{- 2}

Apply the fraction rule:

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

= - \frac{2}{2}

Apply rule

\frac{a}{a} = 1

= - 1

The solutions to the quadratic equation are:

u = - 4, u = - 1

Substitute back

u = cos (θ)

cos (θ) = - 4, cos (θ) = - 1

cos (θ) = - 4, cos (θ) = - 1

cos (θ) = - 4 :

No Solution

cos (θ) = - 4

- 1 \leq cos (x) \leq 1

No Solution

cos (θ) = - 1 : θ = π + 2 πn

cos (θ) = - 1

General solutions for

cos (θ) = - 1

cos (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} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{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} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

θ = π + 2 πn

θ = π + 2 πn

Combine all the solutions

θ = π + 2 πn

Popular Examples

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

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

cos^2(x)=sin^2(x)

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

sin(x+pi/4)+sin(x-pi/4)=-1

sin (x + \frac{π}{4}) + sin (x - \frac{π}{4}) = - 1

cos(x/4)=0

cos (\frac{x}{4}) = 0

cos(θ)=0.92

cos (θ) = 0.92

Frequently Asked Questions (FAQ)

What is the general solution for sin^2(θ)=5(cos(θ)+1) ?
The general solution for sin^2(θ)=5(cos(θ)+1) is θ=pi+2pin