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cot^2(x)csc^2(x)-cot^2(x)=9

Solution

cot^{2} (x) csc^{2} (x) - cot^{2} (x) = 9

Solution

x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn, x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

Degrees

x = 3 0^{\circ} + 36 0^{\circ} n, x = 15 0^{\circ} + 36 0^{\circ} n, x = 21 0^{\circ} + 36 0^{\circ} n, x = 33 0^{\circ} + 36 0^{\circ} n

Solution steps

cot^{2} (x) csc^{2} (x) - cot^{2} (x) = 9

Subtract

9

from both sides

cot^{2} (x) csc^{2} (x) - cot^{2} (x) - 9 = 0

Rewrite using trig identities

- 9 - cot^{2} (x) + cot^{2} (x) csc^{2} (x)

Use the Pythagorean identity:

1 + cot^{2} (x) = csc^{2} (x)

cot^{2} (x) = csc^{2} (x) - 1

= - 9 - (csc^{2} (x) - 1) + (csc^{2} (x) - 1) csc^{2} (x)

Simplify

- 9 - (csc^{2} (x) - 1) + (csc^{2} (x) - 1) csc^{2} (x) : csc^{4} (x) - 2 csc^{2} (x) - 8

- 9 - (csc^{2} (x) - 1) + (csc^{2} (x) - 1) csc^{2} (x)

= - 9 - (csc^{2} (x) - 1) + csc^{2} (x) (csc^{2} (x) - 1)

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

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

Distribute parentheses

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

Apply minus-plus rules

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

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

= - 9 - csc^{2} (x) + 1 + (csc^{2} (x) - 1) csc^{2} (x)

Expand

csc^{2} (x) (csc^{2} (x) - 1) : csc^{4} (x) - csc^{2} (x)

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

Apply the distributive law:

a (b - c) = ab - a c

a = csc^{2} (x), b = csc^{2} (x), c = 1

= csc^{2} (x) csc^{2} (x) - csc^{2} (x) \cdot 1

= csc^{2} (x) csc^{2} (x) - 1 \cdot csc^{2} (x)

Simplify

csc^{2} (x) csc^{2} (x) - 1 \cdot csc^{2} (x) : csc^{4} (x) - csc^{2} (x)

csc^{2} (x) csc^{2} (x) - 1 \cdot csc^{2} (x)

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

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

Apply exponent rule:

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

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

= csc^{2 + 2} (x)

Add the numbers:

2 + 2 = 4

= csc^{4} (x)

1 \cdot csc^{2} (x) = csc^{2} (x)

1 \cdot csc^{2} (x)

Multiply:

1 \cdot csc^{2} (x) = csc^{2} (x)

= csc^{2} (x)

= csc^{4} (x) - csc^{2} (x)

= csc^{4} (x) - csc^{2} (x)

= - 9 - csc^{2} (x) + 1 + csc^{4} (x) - csc^{2} (x)

Simplify

- 9 - csc^{2} (x) + 1 + csc^{4} (x) - csc^{2} (x) : csc^{4} (x) - 2 csc^{2} (x) - 8

- 9 - csc^{2} (x) + 1 + csc^{4} (x) - csc^{2} (x)

Group like terms

= - csc^{2} (x) + csc^{4} (x) - csc^{2} (x) - 9 + 1

Add similar elements:

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

= - 2 csc^{2} (x) + csc^{4} (x) - 9 + 1

Add/Subtract the numbers:

- 9 + 1 = - 8

= csc^{4} (x) - 2 csc^{2} (x) - 8

= csc^{4} (x) - 2 csc^{2} (x) - 8

= csc^{4} (x) - 2 csc^{2} (x) - 8

- 8 + csc^{4} (x) - 2 csc^{2} (x) = 0

Solve by substitution

- 8 + csc^{4} (x) - 2 csc^{2} (x) = 0

Let:

csc (x) = u

- 8 + u^{4} - 2 u^{2} = 0

- 8 + u^{4} - 2 u^{2} = 0 : u = 2, u = - 2, u = 2 i, u = - 2 i

- 8 + u^{4} - 2 u^{2} = 0

Write in the standard form

a_{n} x^{n} + \dots + a_{1} x + a_{0} = 0

u^{4} - 2 u^{2} - 8 = 0

Rewrite the equation with

v = u^{2}

and

v^{2} = u^{4}

v^{2} - 2 v - 8 = 0

Solve

v^{2} - 2 v - 8 = 0 : v = 4, v = - 2

v^{2} - 2 v - 8 = 0

Solve with the quadratic formula

v^{2} - 2 v - 8 = 0

Quadratic Equation Formula:

For

a = 1, b = - 2, c = - 8

v_{1, 2} = \frac{- ( - 2 ) \pm ( - 2 ) ^{2} - 4 \cdot 1 \cdot ( - 8 )}{2 \cdot 1}

v_{1, 2} = \frac{- ( - 2 ) \pm ( - 2 ) ^{2} - 4 \cdot 1 \cdot ( - 8 )}{2 \cdot 1}

(- 2)^{2} - 4 \cdot 1 \cdot (- 8) = 6

(- 2)^{2} - 4 \cdot 1 \cdot (- 8)

Apply rule

- (- a) = a

= (- 2)^{2} + 4 \cdot 1 \cdot 8

Apply exponent rule:

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

n

is even

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

= 2^{2} + 4 \cdot 1 \cdot 8

Multiply the numbers:

4 \cdot 1 \cdot 8 = 32

= 2^{2} + 32

2^{2} = 4

= 4 + 32

Add the numbers:

4 + 32 = 36

= 36

Factor the number:

36 = 6^{2}

= 6^{2}

Apply radical rule:

6^{2} = 6

= 6

v_{1, 2} = \frac{- ( - 2 ) \pm 6}{2 \cdot 1}

Separate the solutions

v_{1} = \frac{- ( - 2 ) + 6}{2 \cdot 1}, v_{2} = \frac{- ( - 2 ) - 6}{2 \cdot 1}

v = \frac{- ( - 2 ) + 6}{2 \cdot 1} : 4

\frac{- ( - 2 ) + 6}{2 \cdot 1}

Apply rule

- (- a) = a

= \frac{2 + 6}{2 \cdot 1}

Add the numbers:

2 + 6 = 8

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

Multiply the numbers:

2 \cdot 1 = 2

= \frac{8}{2}

Divide the numbers:

\frac{8}{2} = 4

= 4

v = \frac{- ( - 2 ) - 6}{2 \cdot 1} : - 2

\frac{- ( - 2 ) - 6}{2 \cdot 1}

Apply rule

- (- a) = a

= \frac{2 - 6}{2 \cdot 1}

Subtract the numbers:

2 - 6 = - 4

= \frac{- 4}{2 \cdot 1}

Multiply the numbers:

2 \cdot 1 = 2

= \frac{- 4}{2}

Apply the fraction rule:

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

= - \frac{4}{2}

Divide the numbers:

\frac{4}{2} = 2

= - 2

The solutions to the quadratic equation are:

v = 4, v = - 2

v = 4, v = - 2

Substitute back

v = u^{2},

solve for

u

Solve

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

u^{2} = 4

For

x^{2} = f (a)

the solutions are

x = f (a), - f (a)

u = 4, u = - 4

4 = 2

4

Factor the number:

4 = 2^{2}

= 2^{2}

Apply radical rule:

2^{2} = 2

= 2

- 4 = - 2

- 4

4 = 2

4

Factor the number:

4 = 2^{2}

= 2^{2}

Apply radical rule:

2^{2} = 2

= 2

= - 2

u = 2, u = - 2

Solve

u^{2} = - 2 : u = 2 i, u = - 2 i

u^{2} = - 2

For

x^{2} = f (a)

the solutions are

x = f (a), - f (a)

u = - 2, u = - - 2

Simplify

- 2 : 2 i

- 2

Apply radical rule:

- a = - 1 a

- 2 = - 1 2

= - 1 2

Apply imaginary number rule:

- 1 = i

= 2 i

Simplify

- - 2 : - 2 i

- - 2

Simplify

- 2 : 2 i

- 2

Apply radical rule:

- a = - 1 a

- 2 = - 1 2

= - 1 2

Apply imaginary number rule:

- 1 = i

= 2 i

= - 2 i

u = 2 i, u = - 2 i

The solutions are

u = 2, u = - 2, u = 2 i, u = - 2 i

Substitute back

u = csc (x)

csc (x) = 2, csc (x) = - 2, csc (x) = 2 i, csc (x) = - 2 i

csc (x) = 2, csc (x) = - 2, csc (x) = 2 i, csc (x) = - 2 i

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

csc (x) = 2

General solutions for

csc (x) = 2

csc (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} csc (x) Undefiend 22 \frac{2 3}{3} 1 \frac{2 3}{3} 22 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} csc (x) Undefiend - 2 - 2 - \frac{2 3}{3} - 1 - \frac{2 3}{3} - 2 - 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

csc (x) = - 2 : x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

csc (x) = - 2

General solutions for

csc (x) = - 2

csc (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} csc (x) Undefiend 22 \frac{2 3}{3} 1 \frac{2 3}{3} 22 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} csc (x) Undefiend - 2 - 2 - \frac{2 3}{3} - 1 - \frac{2 3}{3} - 2 - 2

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

csc (x) = 2 i :

No Solution

csc (x) = 2 i

No Solution

csc (x) = - 2 i :

No Solution

csc (x) = - 2 i

No Solution

Combine all the solutions

x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn, x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

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