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Popular Trigonometry >

tan^2(θ)sec^2(θ)=3

Solution

tan^{2} (θ) sec^{2} (θ) = 3

Solution

θ = 0.85133 \dots + 2 πn, θ = 2 π - 0.85133 \dots + 2 πn, θ = 2.29026 \dots + 2 πn, θ = - 2.29026 \dots + 2 πn

Degrees

θ = 48.77764 \dots^{\circ} + 36 0^{\circ} n, θ = 311.22235 \dots^{\circ} + 36 0^{\circ} n, θ = 131.22235 \dots^{\circ} + 36 0^{\circ} n, θ = - 131.22235 \dots^{\circ} + 36 0^{\circ} n

Solution steps

tan^{2} (θ) sec^{2} (θ) = 3

Subtract

3

from both sides

tan^{2} (θ) sec^{2} (θ) - 3 = 0

Rewrite using trig identities

- 3 + sec^{2} (θ) tan^{2} (θ)

Use the Pythagorean identity:

tan^{2} (x) + 1 = sec^{2} (x)

tan^{2} (x) = sec^{2} (x) - 1

= - 3 + sec^{2} (θ) (sec^{2} (θ) - 1)

- 3 + (- 1 + sec^{2} (θ)) sec^{2} (θ) = 0

Solve by substitution

- 3 + (- 1 + sec^{2} (θ)) sec^{2} (θ) = 0

Let:

sec (θ) = u

- 3 + (- 1 + u^{2}) u^{2} = 0

- 3 + (- 1 + u^{2}) u^{2} = 0 : u = \frac{1 + 13}{2}, u = - \frac{1 + 13}{2}, u = \frac{1 - 13}{2}, u = - \frac{1 - 13}{2}

- 3 + (- 1 + u^{2}) u^{2} = 0

Expand

- 3 + (- 1 + u^{2}) u^{2} : - 3 - u^{2} + u^{4}

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

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

Expand

u^{2} (- 1 + u^{2}) : - u^{2} + u^{4}

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

Apply the distributive law:

a (b + c) = ab + a c

a = u^{2}, b = - 1, c = u^{2}

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

Apply minus-plus rules

+ (- a) = - a

= - 1 \cdot u^{2} + u^{2} u^{2}

Simplify

- 1 \cdot u^{2} + u^{2} u^{2} : - u^{2} + u^{4}

- 1 \cdot u^{2} + u^{2} u^{2}

1 \cdot u^{2} = u^{2}

1 \cdot u^{2}

Multiply:

1 \cdot u^{2} = u^{2}

= u^{2}

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

u^{2} u^{2}

Apply exponent rule:

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

u^{2} u^{2} = u^{2 + 2}

= u^{2 + 2}

Add the numbers:

2 + 2 = 4

= u^{4}

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

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

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

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

Write in the standard form

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

u^{4} - u^{2} - 3 = 0

Rewrite the equation with

v = u^{2}

and

v^{2} = u^{4}

v^{2} - v - 3 = 0

Solve

v^{2} - v - 3 = 0 : v = \frac{1 + 13}{2}, v = \frac{1 - 13}{2}

v^{2} - v - 3 = 0

Solve with the quadratic formula

v^{2} - v - 3 = 0

Quadratic Equation Formula:

For

a = 1, b = - 1, c = - 3

v_{1, 2} = \frac{- ( - 1 ) \pm ( - 1 ) ^{2} - 4 \cdot 1 \cdot ( - 3 )}{2 \cdot 1}

v_{1, 2} = \frac{- ( - 1 ) \pm ( - 1 ) ^{2} - 4 \cdot 1 \cdot ( - 3 )}{2 \cdot 1}

(- 1)^{2} - 4 \cdot 1 \cdot (- 3) = 13

(- 1)^{2} - 4 \cdot 1 \cdot (- 3)

Apply rule

- (- a) = a

= (- 1)^{2} + 4 \cdot 1 \cdot 3

(- 1)^{2} = 1

(- 1)^{2}

Apply exponent rule:

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

n

is even

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

= 1^{2}

Apply rule

1^{a} = 1

= 1

4 \cdot 1 \cdot 3 = 12

4 \cdot 1 \cdot 3

Multiply the numbers:

4 \cdot 1 \cdot 3 = 12

= 12

= 1 + 12

Add the numbers:

1 + 12 = 13

= 13

v_{1, 2} = \frac{- ( - 1 ) \pm 13}{2 \cdot 1}

Separate the solutions

v_{1} = \frac{- ( - 1 ) + 13}{2 \cdot 1}, v_{2} = \frac{- ( - 1 ) - 13}{2 \cdot 1}

v = \frac{- ( - 1 ) + 13}{2 \cdot 1} : \frac{1 + 13}{2}

\frac{- ( - 1 ) + 13}{2 \cdot 1}

Apply rule

- (- a) = a

= \frac{1 + 13}{2 \cdot 1}

Multiply the numbers:

2 \cdot 1 = 2

= \frac{1 + 13}{2}

v = \frac{- ( - 1 ) - 13}{2 \cdot 1} : \frac{1 - 13}{2}

\frac{- ( - 1 ) - 13}{2 \cdot 1}

Apply rule

- (- a) = a

= \frac{1 - 13}{2 \cdot 1}

Multiply the numbers:

2 \cdot 1 = 2

= \frac{1 - 13}{2}

The solutions to the quadratic equation are:

v = \frac{1 + 13}{2}, v = \frac{1 - 13}{2}

v = \frac{1 + 13}{2}, v = \frac{1 - 13}{2}

Substitute back

v = u^{2},

solve for

u

Solve

u^{2} = \frac{1 + 13}{2} : u = \frac{1 + 13}{2}, u = - \frac{1 + 13}{2}

u^{2} = \frac{1 + 13}{2}

For

x^{2} = f (a)

the solutions are

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

u = \frac{1 + 13}{2}, u = - \frac{1 + 13}{2}

Solve

u^{2} = \frac{1 - 13}{2} : u = \frac{1 - 13}{2}, u = - \frac{1 - 13}{2}

u^{2} = \frac{1 - 13}{2}

For

x^{2} = f (a)

the solutions are

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

u = \frac{1 - 13}{2}, u = - \frac{1 - 13}{2}

The solutions are

u = \frac{1 + 13}{2}, u = - \frac{1 + 13}{2}, u = \frac{1 - 13}{2}, u = - \frac{1 - 13}{2}

Substitute back

u = sec (θ)

sec (θ) = \frac{1 + 13}{2}, sec (θ) = - \frac{1 + 13}{2}, sec (θ) = \frac{1 - 13}{2}, sec (θ) = - \frac{1 - 13}{2}

sec (θ) = \frac{1 + 13}{2}, sec (θ) = - \frac{1 + 13}{2}, sec (θ) = \frac{1 - 13}{2}, sec (θ) = - \frac{1 - 13}{2}

sec (θ) = \frac{1 + 13}{2} : θ = arcsec \frac{1 + 13}{2} + 2 πn, θ = 2 π - arcsec \frac{1 + 13}{2} + 2 πn

sec (θ) = \frac{1 + 13}{2}

Apply trig inverse properties

sec (θ) = \frac{1 + 13}{2}

General solutions for

sec (θ) = \frac{1 + 13}{2}

sec (x) = a \Rightarrow x = arcsec (a) + 2 πn, x = 2 π - arcsec (a) + 2 πn

θ = arcsec \frac{1 + 13}{2} + 2 πn, θ = 2 π - arcsec \frac{1 + 13}{2} + 2 πn

θ = arcsec \frac{1 + 13}{2} + 2 πn, θ = 2 π - arcsec \frac{1 + 13}{2} + 2 πn

sec (θ) = - \frac{1 + 13}{2} : θ = arcsec - \frac{1 + 13}{2} + 2 πn, θ = - arcsec - \frac{1 + 13}{2} + 2 πn

sec (θ) = - \frac{1 + 13}{2}

Apply trig inverse properties

sec (θ) = - \frac{1 + 13}{2}

General solutions for

sec (θ) = - \frac{1 + 13}{2}

sec (x) = - a \Rightarrow x = arcsec (- a) + 2 πn, x = - arcsec (- a) + 2 πn

θ = arcsec - \frac{1 + 13}{2} + 2 πn, θ = - arcsec - \frac{1 + 13}{2} + 2 πn

θ = arcsec - \frac{1 + 13}{2} + 2 πn, θ = - arcsec - \frac{1 + 13}{2} + 2 πn

sec (θ) = \frac{1 - 13}{2} : θ = arcsec \frac{1 - 13}{2} + 2 πn, θ = - arcsec \frac{1 - 13}{2} + 2 πn

sec (θ) = \frac{1 - 13}{2}

Apply trig inverse properties

sec (θ) = \frac{1 - 13}{2}

General solutions for

sec (θ) = \frac{1 - 13}{2}

sec (x) = a \Rightarrow x = arcsec (a) + 2 πn, x = - arcsec (a) + 2 πn

θ = arcsec \frac{1 - 13}{2} + 2 πn, θ = - arcsec \frac{1 - 13}{2} + 2 πn

θ = arcsec \frac{1 - 13}{2} + 2 πn, θ = - arcsec \frac{1 - 13}{2} + 2 πn

sec (θ) = - \frac{1 - 13}{2} : θ = arcsec - \frac{1 - 13}{2} + 2 πn, θ = - arcsec - \frac{1 - 13}{2} + 2 πn

sec (θ) = - \frac{1 - 13}{2}

Apply trig inverse properties

sec (θ) = - \frac{1 - 13}{2}

General solutions for

sec (θ) = - \frac{1 - 13}{2}

sec (x) = a \Rightarrow x = arcsec (a) + 2 πn, x = - arcsec (a) + 2 πn

θ = arcsec - \frac{1 - 13}{2} + 2 πn, θ = - arcsec - \frac{1 - 13}{2} + 2 πn

θ = arcsec - \frac{1 - 13}{2} + 2 πn, θ = - arcsec - \frac{1 - 13}{2} + 2 πn

Combine all the solutions

θ = arcsec \frac{1 + 13}{2} + 2 πn, θ = 2 π - arcsec \frac{1 + 13}{2} + 2 πn, θ = arcsec - \frac{1 + 13}{2} + 2 πn, θ = - arcsec - \frac{1 + 13}{2} + 2 πn, θ = arcsec \frac{1 - 13}{2} + 2 πn, θ = - arcsec \frac{1 - 13}{2} + 2 πn, θ = arcsec - \frac{1 - 13}{2} + 2 πn, θ = - arcsec - \frac{1 - 13}{2} + 2 πn

Since the equation is undefined for:

arcsec \frac{1 - 13}{2} + 2 πn, - arcsec \frac{1 - 13}{2} + 2 πn, arcsec - \frac{1 - 13}{2} + 2 πn, - arcsec - \frac{1 - 13}{2} + 2 πn

θ = arcsec \frac{1 + 13}{2} + 2 πn, θ = 2 π - arcsec \frac{1 + 13}{2} + 2 πn, θ = arcsec - \frac{1 + 13}{2} + 2 πn, θ = - arcsec - \frac{1 + 13}{2} + 2 πn

Show solutions in decimal form

θ = 0.85133 \dots + 2 πn, θ = 2 π - 0.85133 \dots + 2 πn, θ = 2.29026 \dots + 2 πn, θ = - 2.29026 \dots + 2 πn

Graph

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