What is the general solution for csc^2(x)=sec(x) ?

The general solution for csc^2(x)=sec(x) is x=0.90455…+2pin,x=2pi-0.90455…+2pin

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Popular >

csc^2(x)=sec(x)

Solution

csc^{2} (x) = sec (x)

Solution

x = 0.90455 \dots + 2 πn, x = 2 π - 0.90455 \dots + 2 πn

Degrees

x = 51.82729 \dots^{\circ} + 36 0^{\circ} n, x = 308.17270 \dots^{\circ} + 36 0^{\circ} n

Solution steps

csc^{2} (x) = sec (x)

Subtract

sec (x)

from both sides

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

Express with sin, cos

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

Simplify

(\frac{1}{sin ( x )})^{2} - \frac{1}{cos ( x )} : \frac{cos ( x ) - sin ^{2} ( x )}{sin ^{2} ( x ) cos ( x )}

(\frac{1}{sin ( x )})^{2} - \frac{1}{cos ( x )}

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

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

Apply exponent rule:

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

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

Apply rule

1^{a} = 1

1^{2} = 1

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

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

Least Common Multiplier of

sin^{2} (x), cos (x) : sin^{2} (x) cos (x)

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

Lowest Common Multiplier (LCM)

Compute an expression comprised of factors that appear either in

sin^{2} (x)

cos (x)

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

Adjust Fractions based on the LCM

Multiply each numerator by the same amount needed to multiply its

corresponding denominator to turn it into the LCM

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

For

\frac{1}{sin ^{2} ( x )} :

multiply the denominator and numerator by

cos (x)

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

For

\frac{1}{cos ( x )} :

multiply the denominator and numerator by

sin^{2} (x)

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

= \frac{cos ( x )}{sin ^{2} ( x ) cos ( x )} - \frac{sin ^{2} ( x )}{sin ^{2} ( x ) cos ( x )}

Since the denominators are equal, combine the fractions:

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

= \frac{cos ( x ) - sin ^{2} ( x )}{sin ^{2} ( x ) cos ( x )}

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

\frac{f ( x )}{g ( x )} = 0 \Rightarrow f (x) = 0

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

Add

sin^{2} (x)

to both sides

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

Square both sides

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

Subtract

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

from both sides

cos^{2} (x) - sin^{4} (x) = 0

Factor

cos^{2} (x) - sin^{4} (x) : (cos (x) + sin^{2} (x)) (cos (x) - sin^{2} (x))

cos^{2} (x) - sin^{4} (x)

Apply exponent rule:

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

sin^{4} (x) = (sin^{2} (x))^{2}

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

Apply Difference of Two Squares Formula:

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

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

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

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

Solving each part separately

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

cos (x) + sin^{2} (x) = 0 : x = arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = - arccos (- \frac{- 1 + 5}{2}) + 2 πn

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

Rewrite using trig identities

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

Use the Pythagorean identity:

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

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

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

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

Solve by substitution

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

Let:

cos (x) = u

1 + u - u^{2} = 0

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

1 + u - u^{2} = 0

Write in the standard form

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

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

Solve with the quadratic formula

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

Quadratic Equation Formula:

For

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

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

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

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

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

Apply rule

1^{a} = 1

1^{2} = 1

= 1 - 4 (- 1) \cdot 1

Apply rule

- (- a) = a

= 1 + 4 \cdot 1 \cdot 1

Multiply the numbers:

4 \cdot 1 \cdot 1 = 4

= 1 + 4

Add the numbers:

1 + 4 = 5

= 5

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

Separate the solutions

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

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

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

Remove parentheses:

(- a) = - a

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

Multiply the numbers:

2 \cdot 1 = 2

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

Apply the fraction rule:

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

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

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

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

Remove parentheses:

(- a) = - a

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

Multiply the numbers:

2 \cdot 1 = 2

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

Apply the fraction rule:

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

- 1 - 5 = - (1 + 5)

= \frac{1 + 5}{2}

The solutions to the quadratic equation are:

u = - \frac{- 1 + 5}{2}, u = \frac{1 + 5}{2}

Substitute back

u = cos (x)

cos (x) = - \frac{- 1 + 5}{2}, cos (x) = \frac{1 + 5}{2}

cos (x) = - \frac{- 1 + 5}{2}, cos (x) = \frac{1 + 5}{2}

cos (x) = - \frac{- 1 + 5}{2} : x = arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = - arccos (- \frac{- 1 + 5}{2}) + 2 πn

cos (x) = - \frac{- 1 + 5}{2}

Apply trig inverse properties

cos (x) = - \frac{- 1 + 5}{2}

General solutions for

cos (x) = - \frac{- 1 + 5}{2}

cos (x) = - a \Rightarrow x = arccos (- a) + 2 πn, x = - arccos (- a) + 2 πn

x = arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = - arccos (- \frac{- 1 + 5}{2}) + 2 πn

x = arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = - arccos (- \frac{- 1 + 5}{2}) + 2 πn

cos (x) = \frac{1 + 5}{2} :

No Solution

cos (x) = \frac{1 + 5}{2}

- 1 \leq cos (x) \leq 1

No Solution

Combine all the solutions

x = arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = - arccos (- \frac{- 1 + 5}{2}) + 2 πn

cos (x) - sin^{2} (x) = 0 : x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

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

Rewrite using trig identities

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

Use the Pythagorean identity:

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

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

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

- (1 - cos^{2} (x)) : - 1 + cos^{2} (x)

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

Distribute parentheses

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

Apply minus-plus rules

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

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

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

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

Solve by substitution

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

Let:

cos (x) = u

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

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

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

Write in the standard form

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

u^{2} + u - 1 = 0

Solve with the quadratic formula

u^{2} + u - 1 = 0

Quadratic Equation Formula:

For

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

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

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

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

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

Apply rule

1^{a} = 1

1^{2} = 1

= 1 - 4 \cdot 1 \cdot (- 1)

Apply rule

- (- a) = a

= 1 + 4 \cdot 1 \cdot 1

Multiply the numbers:

4 \cdot 1 \cdot 1 = 4

= 1 + 4

Add the numbers:

1 + 4 = 5

= 5

u_{1, 2} = \frac{- 1 \pm 5}{2 \cdot 1}

Separate the solutions

u_{1} = \frac{- 1 + 5}{2 \cdot 1}, u_{2} = \frac{- 1 - 5}{2 \cdot 1}

u = \frac{- 1 + 5}{2 \cdot 1} : \frac{- 1 + 5}{2}

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

Multiply the numbers:

2 \cdot 1 = 2

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

u = \frac{- 1 - 5}{2 \cdot 1} : \frac{- 1 - 5}{2}

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

Multiply the numbers:

2 \cdot 1 = 2

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

The solutions to the quadratic equation are:

u = \frac{- 1 + 5}{2}, u = \frac{- 1 - 5}{2}

Substitute back

u = cos (x)

cos (x) = \frac{- 1 + 5}{2}, cos (x) = \frac{- 1 - 5}{2}

cos (x) = \frac{- 1 + 5}{2}, cos (x) = \frac{- 1 - 5}{2}

cos (x) = \frac{- 1 + 5}{2} : x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

cos (x) = \frac{- 1 + 5}{2}

Apply trig inverse properties

cos (x) = \frac{- 1 + 5}{2}

General solutions for

cos (x) = \frac{- 1 + 5}{2}

cos (x) = a \Rightarrow x = arccos (a) + 2 πn, x = 2 π - arccos (a) + 2 πn

x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

cos (x) = \frac{- 1 - 5}{2} :

No Solution

cos (x) = \frac{- 1 - 5}{2}

- 1 \leq cos (x) \leq 1

No Solution

Combine all the solutions

x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

Combine all the solutions

x = arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = - arccos (- \frac{- 1 + 5}{2}) + 2 πn, x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

Verify solutions by plugging them into the original equation

Check the solutions by plugging them into

csc^{2} (x) = sec (x)

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

Check the solution

arccos (- \frac{- 1 + 5}{2}) + 2 πn :

False

arccos (- \frac{- 1 + 5}{2}) + 2 πn

Plug in

n = 1

arccos (- \frac{- 1 + 5}{2}) + 2 π 1

For

csc^{2} (x) = sec (x)

plug in

x = arccos (- \frac{- 1 + 5}{2}) + 2 π 1

csc^{2} (arccos (- \frac{- 1 + 5}{2}) + 2 π 1) = sec (arccos (- \frac{- 1 + 5}{2}) + 2 π 1)

Refine

1.61803 \dots = - 1.61803 \dots

\Rightarrow False

Check the solution

- arccos (- \frac{- 1 + 5}{2}) + 2 πn :

False

- arccos (- \frac{- 1 + 5}{2}) + 2 πn

Plug in

n = 1

- arccos (- \frac{- 1 + 5}{2}) + 2 π 1

For

csc^{2} (x) = sec (x)

plug in

x = - arccos (- \frac{- 1 + 5}{2}) + 2 π 1

csc^{2} (- arccos (- \frac{- 1 + 5}{2}) + 2 π 1) = sec (- arccos (- \frac{- 1 + 5}{2}) + 2 π 1)

Refine

1.61803 \dots = - 1.61803 \dots

\Rightarrow False

Check the solution

arccos (\frac{- 1 + 5}{2}) + 2 πn :

True

arccos (\frac{- 1 + 5}{2}) + 2 πn

Plug in

n = 1

arccos (\frac{- 1 + 5}{2}) + 2 π 1

For

csc^{2} (x) = sec (x)

plug in

x = arccos (\frac{- 1 + 5}{2}) + 2 π 1

csc^{2} (arccos (\frac{- 1 + 5}{2}) + 2 π 1) = sec (arccos (\frac{- 1 + 5}{2}) + 2 π 1)

Refine

1.61803 \dots = 1.61803 \dots

\Rightarrow True

Check the solution

2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn :

True

2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

Plug in

n = 1

2 π - arccos (\frac{- 1 + 5}{2}) + 2 π 1

For

csc^{2} (x) = sec (x)

plug in

x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 π 1

csc^{2} (2 π - arccos (\frac{- 1 + 5}{2}) + 2 π 1) = sec (2 π - arccos (\frac{- 1 + 5}{2}) + 2 π 1)

Refine

1.61803 \dots = 1.61803 \dots

\Rightarrow True

x = arccos (\frac{- 1 + 5}{2}) + 2 πn, x = 2 π - arccos (\frac{- 1 + 5}{2}) + 2 πn

Show solutions in decimal form

x = 0.90455 \dots + 2 πn, x = 2 π - 0.90455 \dots + 2 πn

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Frequently Asked Questions (FAQ)

What is the general solution for csc^2(x)=sec(x) ?
The general solution for csc^2(x)=sec(x) is x=0.90455…+2pin,x=2pi-0.90455…+2pin