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Popular >

2sec^2(x)=tan^2(x)+2sec(x)+4

Solution

2 sec^{2} (x) = tan^{2} (x) + 2 sec (x) + 4

Solution

x = 1.23095 \dots + 2 πn, x = 2 π - 1.23095 \dots + 2 πn, x = π + 2 πn

Degrees

x = 70.52877 \dots^{\circ} + 36 0^{\circ} n, x = 289.47122 \dots^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n

Solution steps

2 sec^{2} (x) = tan^{2} (x) + 2 sec (x) + 4

Subtract

tan^{2} (x) + 2 sec (x) + 4

from both sides

2 sec^{2} (x) - tan^{2} (x) - 2 sec (x) - 4 = 0

Rewrite using trig identities

- 4 - tan^{2} (x) - 2 sec (x) + 2 sec^{2} (x)

Use the Pythagorean identity:

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

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

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

Simplify

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

- 4 - (sec^{2} (x) - 1) - 2 sec (x) + 2 sec^{2} (x)

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

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

Distribute parentheses

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

Apply minus-plus rules

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

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

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

Simplify

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

- 4 - sec^{2} (x) + 1 - 2 sec (x) + 2 sec^{2} (x)

Group like terms

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

Add similar elements:

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

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

Add/Subtract the numbers:

- 4 + 1 = - 3

= sec^{2} (x) - 2 sec (x) - 3

= sec^{2} (x) - 2 sec (x) - 3

= sec^{2} (x) - 2 sec (x) - 3

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

Solve by substitution

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

Let:

sec (x) = u

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

- 3 + u^{2} - 2 u = 0 : u = 3, u = - 1

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

Write in the standard form

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

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

Solve with the quadratic formula

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

Quadratic Equation Formula:

For

a = 1, b = - 2, c = - 3

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

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

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

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

Apply rule

- (- a) = a

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

Apply exponent rule:

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

n

is even

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

= 2^{2} + 4 \cdot 1 \cdot 3

Multiply the numbers:

4 \cdot 1 \cdot 3 = 12

= 2^{2} + 12

2^{2} = 4

= 4 + 12

Add the numbers:

4 + 12 = 16

= 16

Factor the number:

16 = 4^{2}

= 4^{2}

Apply radical rule:

4^{2} = 4

= 4

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

Separate the solutions

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

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

\frac{- ( - 2 ) + 4}{2 \cdot 1}

Apply rule

- (- a) = a

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

Add the numbers:

2 + 4 = 6

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

Multiply the numbers:

2 \cdot 1 = 2

= \frac{6}{2}

Divide the numbers:

\frac{6}{2} = 3

= 3

u = \frac{- ( - 2 ) - 4}{2 \cdot 1} : - 1

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

Apply rule

- (- a) = a

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

Subtract the numbers:

2 - 4 = - 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 = 3, u = - 1

Substitute back

u = sec (x)

sec (x) = 3, sec (x) = - 1

sec (x) = 3, sec (x) = - 1

sec (x) = 3 : x = arcsec (3) + 2 πn, x = 2 π - arcsec (3) + 2 πn

sec (x) = 3

Apply trig inverse properties

sec (x) = 3

General solutions for

sec (x) = 3

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

x = arcsec (3) + 2 πn, x = 2 π - arcsec (3) + 2 πn

x = arcsec (3) + 2 πn, x = 2 π - arcsec (3) + 2 πn

sec (x) = - 1 : x = π + 2 πn

sec (x) = - 1

General solutions for

sec (x) = - 1

sec (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} sec (x) 1 \frac{2 3}{3} 22 Undefined - 2 - 2 - \frac{2 3}{3} 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} sec (x) - 1 - \frac{2 3}{3} - 2 - 2 Undefined 22 \frac{2 3}{3}

x = π + 2 πn

x = π + 2 πn

Combine all the solutions

x = arcsec (3) + 2 πn, x = 2 π - arcsec (3) + 2 πn, x = π + 2 πn

Show solutions in decimal form

x = 1.23095 \dots + 2 πn, x = 2 π - 1.23095 \dots + 2 πn, x = π + 2 πn

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