What is the general solution for (cos(a))/(1+sin(a))=sec(a) ?

The general solution for (cos(a))/(1+sin(a))=sec(a) is a=2pin,a=pi+2pin

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(cos(a))/(1+sin(a))=sec(a)

Solution

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

Solution

a = 2 πn, a = π + 2 πn

Degrees

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

Solution steps

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

Subtract

sec (a)

from both sides

\frac{cos ( a )}{1 + sin ( a )} - sec (a) = 0

Simplify

\frac{cos ( a )}{1 + sin ( a )} - sec (a) : \frac{cos ( a ) - sec ( a ) ( 1 + sin ( a ) )}{1 + sin ( a )}

\frac{cos ( a )}{1 + sin ( a )} - sec (a)

Convert element to fraction:

sec (a) = \frac{sec ( a ) ( 1 + sin ( a ) )}{1 + sin ( a )}

= \frac{cos ( a )}{1 + sin ( a )} - \frac{sec ( a ) ( 1 + sin ( a ) )}{1 + sin ( a )}

Since the denominators are equal, combine the fractions:

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

= \frac{cos ( a ) - sec ( a ) ( 1 + sin ( a ) )}{1 + sin ( a )}

\frac{cos ( a ) - sec ( a ) ( 1 + sin ( a ) )}{1 + sin ( a )} = 0

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

cos (a) - sec (a) (1 + sin (a)) = 0

Express with sin, cos

cos (a) - \frac{1}{cos ( a )} (1 + sin (a)) = 0

Simplify

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

cos (a) - \frac{1}{cos ( a )} (1 + sin (a))

\frac{1}{cos ( a )} (1 + sin (a)) = \frac{1 + sin ( a )}{cos ( a )}

\frac{1}{cos ( a )} (1 + sin (a))

Multiply fractions:

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

= \frac{1 \cdot ( 1 + sin ( a ) )}{cos ( a )}

1 \cdot (1 + sin (a)) = 1 + sin (a)

1 \cdot (1 + sin (a))

Multiply:

1 \cdot (1 + sin (a)) = (1 + sin (a))

= (1 + sin (a))

Remove parentheses:

(a) = a

= 1 + sin (a)

= \frac{1 + sin ( a )}{cos ( a )}

= cos (a) - \frac{sin ( a ) + 1}{cos ( a )}

Convert element to fraction:

cos (a) = \frac{cos ( a ) cos ( a )}{cos ( a )}

= \frac{cos ( a ) cos ( a )}{cos ( a )} - \frac{1 + sin ( a )}{cos ( a )}

Since the denominators are equal, combine the fractions:

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

= \frac{cos ( a ) cos ( a ) - ( 1 + sin ( a ) )}{cos ( a )}

cos (a) cos (a) - (1 + sin (a)) = cos^{2} (a) - (1 + sin (a))

cos (a) cos (a) - (1 + sin (a))

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

cos (a) cos (a)

Apply exponent rule:

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

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

= cos^{1 + 1} (a)

Add the numbers:

1 + 1 = 2

= cos^{2} (a)

= cos^{2} (a) - (sin (a) + 1)

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

- (1 + sin (a)) : - 1 - sin (a)

- (1 + sin (a))

Distribute parentheses

= - (1) - (sin (a))

Apply minus-plus rules

+ (- a) = - a

= - 1 - sin (a)

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

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

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

cos^{2} (a) - 1 - sin (a) = 0

Add

sin (a)

to both sides

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

Square both sides

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

Subtract

sin^{2} (a)

from both sides

(cos^{2} (a) - 1)^{2} - sin^{2} (a) = 0

Factor

(cos^{2} (a) - 1)^{2} - sin^{2} (a) : (cos^{2} (a) - 1 + sin (a)) (cos^{2} (a) - 1 - sin (a))

(cos^{2} (a) - 1)^{2} - sin^{2} (a)

Apply Difference of Two Squares Formula:

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

(cos^{2} (a) - 1)^{2} - sin^{2} (a) = ((cos^{2} (a) - 1) + sin (a)) ((cos^{2} (a) - 1) - sin (a))

= ((cos^{2} (a) - 1) + sin (a)) ((cos^{2} (a) - 1) - sin (a))

Refine

= (cos^{2} (a) + sin (a) - 1) (cos^{2} (a) - sin (a) - 1)

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

Solving each part separately

cos^{2} (a) - 1 + sin (a) = 0 or cos^{2} (a) - 1 - sin (a) = 0

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

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

Rewrite using trig identities

- 1 + cos^{2} (a) + sin (a)

Use the Pythagorean identity:

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

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

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

sin (a) - sin^{2} (a) = 0

Solve by substitution

sin (a) - sin^{2} (a) = 0

Let:

sin (a) = u

u - u^{2} = 0

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

u - u^{2} = 0

Write in the standard form

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

- u^{2} + u = 0

Solve with the quadratic formula

- u^{2} + u = 0

Quadratic Equation Formula:

For

a = - 1, b = 1, c = 0

u_{1, 2} = \frac{- 1 \pm 1 ^{2} - 4 ( - 1 ) \cdot 0}{2 ( - 1 )}

u_{1, 2} = \frac{- 1 \pm 1 ^{2} - 4 ( - 1 ) \cdot 0}{2 ( - 1 )}

1^{2} - 4 (- 1) \cdot 0 = 1

1^{2} - 4 (- 1) \cdot 0

Apply rule

1^{a} = 1

1^{2} = 1

= 1 - 4 (- 1) \cdot 0

Apply rule

- (- a) = a

= 1 + 4 \cdot 1 \cdot 0

Apply rule

0 \cdot a = 0

= 1 + 0

Add the numbers:

1 + 0 = 1

= 1

Apply rule

1 = 1

= 1

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

Separate the solutions

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

u = \frac{- 1 + 1}{2 ( - 1 )} : 0

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

Remove parentheses:

(- a) = - a

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

Add/Subtract the numbers:

- 1 + 1 = 0

= \frac{0}{- 2 \cdot 1}

Multiply the numbers:

2 \cdot 1 = 2

= \frac{0}{- 2}

Apply the fraction rule:

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

= - \frac{0}{2}

Apply rule

\frac{0}{a} = 0, a \neq = 0

= - 0

= 0

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

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

Remove parentheses:

(- a) = - a

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

Subtract the numbers:

- 1 - 1 = - 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 = 0, u = 1

Substitute back

u = sin (a)

sin (a) = 0, sin (a) = 1

sin (a) = 0, sin (a) = 1

sin (a) = 0 : a = 2 πn, a = π + 2 πn

sin (a) = 0

General solutions for

sin (a) = 0

sin (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} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 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} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

a = 0 + 2 πn, a = π + 2 πn

a = 0 + 2 πn, a = π + 2 πn

Solve

a = 0 + 2 πn : a = 2 πn

a = 0 + 2 πn

0 + 2 πn = 2 πn

a = 2 πn

a = 2 πn, a = π + 2 πn

sin (a) = 1 : a = \frac{π}{2} + 2 πn

sin (a) = 1

General solutions for

sin (a) = 1

sin (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} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 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} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

a = \frac{π}{2} + 2 πn

a = \frac{π}{2} + 2 πn

Combine all the solutions

a = 2 πn, a = π + 2 πn, a = \frac{π}{2} + 2 πn

cos^{2} (a) - 1 - sin (a) = 0 : a = \frac{3 π}{2} + 2 πn, a = 2 πn, a = π + 2 πn

cos^{2} (a) - 1 - sin (a) = 0

Rewrite using trig identities

- 1 + cos^{2} (a) - sin (a)

Use the Pythagorean identity:

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

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

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

- sin (a) - sin^{2} (a) = 0

Solve by substitution

- sin (a) - sin^{2} (a) = 0

Let:

sin (a) = u

- u - u^{2} = 0

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

- u - u^{2} = 0

Write in the standard form

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

- u^{2} - u = 0

Solve with the quadratic formula

- u^{2} - u = 0

Quadratic Equation Formula:

For

a = - 1, b = - 1, c = 0

u_{1, 2} = \frac{- ( - 1 ) \pm ( - 1 ) ^{2} - 4 ( - 1 ) \cdot 0}{2 ( - 1 )}

u_{1, 2} = \frac{- ( - 1 ) \pm ( - 1 ) ^{2} - 4 ( - 1 ) \cdot 0}{2 ( - 1 )}

(- 1)^{2} - 4 (- 1) \cdot 0 = 1

(- 1)^{2} - 4 (- 1) \cdot 0

Apply rule

- (- a) = a

= (- 1)^{2} + 4 \cdot 1 \cdot 0

(- 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 0 = 0

4 \cdot 1 \cdot 0

Apply rule

0 \cdot a = 0

= 0

= 1 + 0

Add the numbers:

1 + 0 = 1

= 1

Apply rule

1 = 1

= 1

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

Separate the solutions

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

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

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

Remove parentheses:

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

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

Add the numbers:

1 + 1 = 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

u = \frac{- ( - 1 ) - 1}{2 ( - 1 )} : 0

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

Remove parentheses:

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

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

Subtract the numbers:

1 - 1 = 0

= \frac{0}{- 2 \cdot 1}

Multiply the numbers:

2 \cdot 1 = 2

= \frac{0}{- 2}

Apply the fraction rule:

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

= - \frac{0}{2}

Apply rule

\frac{0}{a} = 0, a \neq = 0

= - 0

= 0

The solutions to the quadratic equation are:

u = - 1, u = 0

Substitute back

u = sin (a)

sin (a) = - 1, sin (a) = 0

sin (a) = - 1, sin (a) = 0

sin (a) = - 1 : a = \frac{3 π}{2} + 2 πn

sin (a) = - 1

General solutions for

sin (a) = - 1

sin (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} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 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} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

a = \frac{3 π}{2} + 2 πn

a = \frac{3 π}{2} + 2 πn

sin (a) = 0 : a = 2 πn, a = π + 2 πn

sin (a) = 0

General solutions for

sin (a) = 0

sin (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} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 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} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

a = 0 + 2 πn, a = π + 2 πn

a = 0 + 2 πn, a = π + 2 πn

Solve

a = 0 + 2 πn : a = 2 πn

a = 0 + 2 πn

0 + 2 πn = 2 πn

a = 2 πn

a = 2 πn, a = π + 2 πn

Combine all the solutions

a = \frac{3 π}{2} + 2 πn, a = 2 πn, a = π + 2 πn

Combine all the solutions

a = 2 πn, a = π + 2 πn, a = \frac{π}{2} + 2 πn, a = \frac{3 π}{2} + 2 πn

Verify solutions by plugging them into the original equation

Check the solutions by plugging them into

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

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

Check the solution

2 πn :

True

2 πn

Plug in

n = 1

2 π 1

For

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

plug in

a = 2 π 1

\frac{cos ( 2 π 1 )}{1 + sin ( 2 π 1 )} = sec (2 π 1)

Refine

1 = 1

\Rightarrow True

Check the solution

π + 2 πn :

True

π + 2 πn

Plug in

n = 1

π + 2 π 1

For

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

plug in

a = π + 2 π 1

\frac{cos ( π + 2 π 1 )}{1 + sin ( π + 2 π 1 )} = sec (π + 2 π 1)

Refine

- 1 = - 1

\Rightarrow True

Check the solution

\frac{π}{2} + 2 πn :

False

\frac{π}{2} + 2 πn

Plug in

n = 1

\frac{π}{2} + 2 π 1

For

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

plug in

a = \frac{π}{2} + 2 π 1

\frac{cos ( \frac{π}{2} + 2 π 1 )}{1 + sin ( \frac{π}{2} + 2 π 1 )} = sec (\frac{π}{2} + 2 π 1)

Refine

0 = \infty

\Rightarrow False

Check the solution

\frac{3 π}{2} + 2 πn :

False

\frac{3 π}{2} + 2 πn

Plug in

n = 1

\frac{3 π}{2} + 2 π 1

For

\frac{cos ( a )}{1 + sin ( a )} = sec (a)

plug in

a = \frac{3 π}{2} + 2 π 1

\frac{cos ( \frac{3 π}{2} + 2 π 1 )}{1 + sin ( \frac{3 π}{2} + 2 π 1 )} = sec (\frac{3 π}{2} + 2 π 1)

Undefined

\Rightarrow False

a = 2 πn, a = π + 2 πn

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Frequently Asked Questions (FAQ)

What is the general solution for (cos(a))/(1+sin(a))=sec(a) ?
The general solution for (cos(a))/(1+sin(a))=sec(a) is a=2pin,a=pi+2pin