What is the general solution for 5sec(x)-2=3cos(x) ?

The general solution for 5sec(x)-2=3cos(x) is x=2pin

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5sec(x)-2=3cos(x)

Solution

5 sec (x) - 2 = 3 cos (x)

Solution

x = 2 πn

Degrees

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

Solution steps

5 sec (x) - 2 = 3 cos (x)

Subtract

3 cos (x)

from both sides

5 sec (x) - 2 - 3 cos (x) = 0

Rewrite using trig identities

- 2 - 3 cos (x) + 5 sec (x)

Use the basic trigonometric identity:

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

= - 2 - 3 \cdot \frac{1}{sec ( x )} + 5 sec (x)

3 \cdot \frac{1}{sec ( x )} = \frac{3}{sec ( x )}

3 \cdot \frac{1}{sec ( x )}

Multiply fractions:

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

= \frac{1 \cdot 3}{sec ( x )}

Multiply the numbers:

1 \cdot 3 = 3

= \frac{3}{sec ( x )}

= - 2 - \frac{3}{sec ( x )} + 5 sec (x)

- 2 - \frac{3}{sec ( x )} + 5 sec (x) = 0

Solve by substitution

- 2 - \frac{3}{sec ( x )} + 5 sec (x) = 0

Let:

sec (x) = u

- 2 - \frac{3}{u} + 5 u = 0

- 2 - \frac{3}{u} + 5 u = 0 : u = 1, u = - \frac{3}{5}

- 2 - \frac{3}{u} + 5 u = 0

Multiply both sides by

u

- 2 - \frac{3}{u} + 5 u = 0

Multiply both sides by

u

- 2 u - \frac{3}{u} u + 5 uu = 0 \cdot u

Simplify

- 2 u - \frac{3}{u} u + 5 uu = 0 \cdot u

Simplify

- \frac{3}{u} u : - 3

- \frac{3}{u} u

Multiply fractions:

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

= - \frac{3 u}{u}

Cancel the common factor:

u

= - 3

Simplify

5 uu : 5 u^{2}

5 uu

Apply exponent rule:

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

uu = u^{1 + 1}

= 5 u^{1 + 1}

Add the numbers:

1 + 1 = 2

= 5 u^{2}

Simplify

0 \cdot u : 0

0 \cdot u

Apply rule

0 \cdot a = 0

= 0

- 2 u - 3 + 5 u^{2} = 0

- 2 u - 3 + 5 u^{2} = 0

- 2 u - 3 + 5 u^{2} = 0

Solve

- 2 u - 3 + 5 u^{2} = 0 : u = 1, u = - \frac{3}{5}

- 2 u - 3 + 5 u^{2} = 0

Write in the standard form

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

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

Solve with the quadratic formula

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

Quadratic Equation Formula:

For

a = 5, b = - 2, c = - 3

u_{1, 2} = \frac{- ( - 2 ) \pm ( - 2 ) ^{2} - 4 \cdot 5 ( - 3 )}{2 \cdot 5}

u_{1, 2} = \frac{- ( - 2 ) \pm ( - 2 ) ^{2} - 4 \cdot 5 ( - 3 )}{2 \cdot 5}

(- 2)^{2} - 4 \cdot 5 (- 3) = 8

(- 2)^{2} - 4 \cdot 5 (- 3)

Apply rule

- (- a) = a

= (- 2)^{2} + 4 \cdot 5 \cdot 3

Apply exponent rule:

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

n

is even

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

= 2^{2} + 4 \cdot 5 \cdot 3

Multiply the numbers:

4 \cdot 5 \cdot 3 = 60

= 2^{2} + 60

2^{2} = 4

= 4 + 60

Add the numbers:

4 + 60 = 64

= 64

Factor the number:

64 = 8^{2}

= 8^{2}

Apply radical rule:

8^{2} = 8

= 8

u_{1, 2} = \frac{- ( - 2 ) \pm 8}{2 \cdot 5}

Separate the solutions

u_{1} = \frac{- ( - 2 ) + 8}{2 \cdot 5}, u_{2} = \frac{- ( - 2 ) - 8}{2 \cdot 5}

u = \frac{- ( - 2 ) + 8}{2 \cdot 5} : 1

\frac{- ( - 2 ) + 8}{2 \cdot 5}

Apply rule

- (- a) = a

= \frac{2 + 8}{2 \cdot 5}

Add the numbers:

2 + 8 = 10

= \frac{10}{2 \cdot 5}

Multiply the numbers:

2 \cdot 5 = 10

= \frac{10}{10}

Apply rule

\frac{a}{a} = 1

= 1

u = \frac{- ( - 2 ) - 8}{2 \cdot 5} : - \frac{3}{5}

\frac{- ( - 2 ) - 8}{2 \cdot 5}

Apply rule

- (- a) = a

= \frac{2 - 8}{2 \cdot 5}

Subtract the numbers:

2 - 8 = - 6

= \frac{- 6}{2 \cdot 5}

Multiply the numbers:

2 \cdot 5 = 10

= \frac{- 6}{10}

Apply the fraction rule:

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

= - \frac{6}{10}

Cancel the common factor:

2

= - \frac{3}{5}

The solutions to the quadratic equation are:

u = 1, u = - \frac{3}{5}

u = 1, u = - \frac{3}{5}

Verify Solutions

Find undefined (singularity) points:

u = 0

Take the denominator(s) of

- 2 - \frac{3}{u} + 5 u

and compare to zero

u = 0

The following points are undefined

u = 0

Combine undefined points with solutions:

u = 1, u = - \frac{3}{5}

Substitute back

u = sec (x)

sec (x) = 1, sec (x) = - \frac{3}{5}

sec (x) = 1, sec (x) = - \frac{3}{5}

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

sec (x) = - \frac{3}{5} :

No Solution

sec (x) = - \frac{3}{5}

sec (x) \leq - 1 or sec (x) \geq 1

No Solution

Combine all the solutions

x = 2 πn

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Frequently Asked Questions (FAQ)

What is the general solution for 5sec(x)-2=3cos(x) ?
The general solution for 5sec(x)-2=3cos(x) is x=2pin