What is the general solution for 1/(cos(x))+sec^2(x)-1-cos(x)=0 ?

The general solution for 1/(cos(x))+sec^2(x)-1-cos(x)=0 is x=pi+2pin,x=2pin

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1/(cos(x))+sec^2(x)-1-cos(x)=0

Solution

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

Solution

x = π + 2 πn, x = 2 πn

Degrees

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

Solution steps

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

Simplify

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

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

Convert element to fraction:

sec^{2} (x) = \frac{sec ^{2} ( x ) cos ( x )}{cos ( x )}, 1 = \frac{1 cos ( x )}{cos ( x )}, cos (x) = \frac{cos ( x ) cos ( x )}{cos ( x )}

= \frac{1}{cos ( x )} + \frac{sec ^{2} ( x ) cos ( x )}{cos ( x )} - \frac{1 \cdot cos ( x )}{cos ( x )} - \frac{cos ( x ) cos ( x )}{cos ( x )}

Since the denominators are equal, combine the fractions:

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

= \frac{1 + sec ^{2} ( x ) cos ( x ) - 1 \cdot cos ( x ) - cos ( x ) cos ( x )}{cos ( x )}

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

1 + sec^{2} (x) cos (x) - 1 \cdot cos (x) - cos (x) cos (x)

1 \cdot cos (x) = cos (x)

1 \cdot cos (x)

Multiply:

1 \cdot cos (x) = cos (x)

= cos (x)

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

cos (x) cos (x)

Apply exponent rule:

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

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

= cos^{1 + 1} (x)

Add the numbers:

1 + 1 = 2

= cos^{2} (x)

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

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

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

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

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

Rewrite using trig identities

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

Use the basic trigonometric identity:

cos (x) = \frac{1}{sec ( x )}

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

Simplify

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

1 - \frac{1}{sec ( x )} - (\frac{1}{sec ( x )})^{2} + \frac{1}{sec ( x )} sec^{2} (x)

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

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

Apply exponent rule:

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

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

Apply rule

1^{a} = 1

1^{2} = 1

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

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

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

Multiply fractions:

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

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

Multiply:

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

= \frac{sec ^{2} ( x )}{sec ( x )}

Cancel the common factor:

sec (x)

= sec (x)

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

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

1 - \frac{1}{sec ^{2} ( x )} - \frac{1}{sec ( x )} + sec (x) = 0

Solve by substitution

1 - \frac{1}{sec ^{2} ( x )} - \frac{1}{sec ( x )} + sec (x) = 0

Let:

sec (x) = u

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

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

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

Multiply by LCM

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

Find Least Common Multiplier of

u^{2}, u : u^{2}

u^{2}, u

Lowest Common Multiplier (LCM)

Compute an expression comprised of factors that appear either in

u^{2}

u

= u^{2}

Multiply by LCM=

u^{2}

1 \cdot u^{2} - \frac{1}{u ^{2}} u^{2} - \frac{1}{u} u^{2} + u u^{2} = 0 \cdot u^{2}

Simplify

1 \cdot u^{2} - \frac{1}{u ^{2}} u^{2} - \frac{1}{u} u^{2} + u u^{2} = 0 \cdot u^{2}

Simplify

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

1 \cdot u^{2}

Multiply:

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

= u^{2}

Simplify

- \frac{1}{u ^{2}} u^{2} : - 1

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

Multiply fractions:

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

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

Cancel the common factor:

u^{2}

= - 1

Simplify

- \frac{1}{u} u^{2} : - u

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

Multiply fractions:

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

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

Multiply:

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

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

Cancel the common factor:

u

= - u

Simplify

u u^{2} : u^{3}

u u^{2}

Apply exponent rule:

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

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

= u^{1 + 2}

Add the numbers:

1 + 2 = 3

= u^{3}

Simplify

0 \cdot u^{2} : 0

0 \cdot u^{2}

Apply rule

0 \cdot a = 0

= 0

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

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

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

Solve

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

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

Write in the standard form

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

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

Factor

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

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

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

Factor out

- 1

from

- u - 1 : - (u + 1)

- u - 1

Factor out common term

- 1

= - (u + 1)

Factor out

u^{2}

from

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

u^{3} + u^{2}

Apply exponent rule:

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

u^{3} = u u^{2}

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

Factor out common term

u^{2}

= u^{2} (u + 1)

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

Factor out common term

u + 1

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

Factor

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

u^{2} - 1

Rewrite

1

1^{2}

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

Apply Difference of Two Squares Formula:

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

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

= (u + 1) (u - 1)

= (u + 1) (u + 1) (u - 1)

Refine

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

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

Using the Zero Factor Principle:

ab = 0

then

a = 0

b = 0

u + 1 = 0 or u - 1 = 0

Solve

u + 1 = 0 : u = - 1

u + 1 = 0

Move

1

to the right side

u + 1 = 0

Subtract

1

from both sides

u + 1 - 1 = 0 - 1

Simplify

u = - 1

u = - 1

Solve

u - 1 = 0 : u = 1

u - 1 = 0

Move

1

to the right side

u - 1 = 0

Add

1

to both sides

u - 1 + 1 = 0 + 1

Simplify

u = 1

u = 1

The solutions are

u = - 1, u = 1

u = - 1, u = 1

Verify Solutions

Find undefined (singularity) points:

u = 0

Take the denominator(s) of

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

and compare to zero

Solve

u^{2} = 0 : u = 0

u^{2} = 0

Apply rule

x^{n} = 0 \Rightarrow x = 0

u = 0

u = 0

The following points are undefined

u = 0

Combine undefined points with solutions:

u = - 1, u = 1

Substitute back

u = sec (x)

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

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

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

sec (x) = 1 : x = 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 = 0 + 2 πn

x = 0 + 2 πn

Solve

x = 0 + 2 πn : x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn

Combine all the solutions

x = π + 2 πn, x = 2 πn

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Frequently Asked Questions (FAQ)

What is the general solution for 1/(cos(x))+sec^2(x)-1-cos(x)=0 ?
The general solution for 1/(cos(x))+sec^2(x)-1-cos(x)=0 is x=pi+2pin,x=2pin