What is the general solution for cos(x1)-cos(x2)=cos(x1-x2) ?

The general solution for cos(x1)-cos(x2)=cos(x1-x2) is x= pi/4+pin,x=(3pi)/4+pin

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cos(x1)-cos(x2)=cos(x1-x2)

Solution

cos (x 1) - cos (x 2) = cos (x 1 - x 2)

Solution

x = \frac{π}{4} + πn, x = \frac{3 π}{4} + πn

Degrees

x = 4 5^{\circ} + 18 0^{\circ} n, x = 13 5^{\circ} + 18 0^{\circ} n

Solution steps

cos (x \cdot 1) - cos (x \cdot 2) = cos (x \cdot 1 - x \cdot 2)

Rewrite using trig identities

cos (x \cdot 1) - cos (x \cdot 2) = cos (x \cdot 1 - x \cdot 2)

Rewrite using trig identities

cos (x \cdot 1 - x \cdot 2)

Use the Angle Difference identity:

cos (s - t) = cos (s) cos (t) + sin (s) sin (t)

= cos (x \cdot 1) cos (x \cdot 2) + sin (x \cdot 1) sin (x \cdot 2)

Simplify

cos (x \cdot 1) cos (x \cdot 2) + sin (x \cdot 1) sin (x \cdot 2) : cos (x) cos (2 x) + sin (x) sin (2 x)

cos (x \cdot 1) cos (x \cdot 2) + sin (x \cdot 1) sin (x \cdot 2)

Multiply:

x \cdot 1 = x

= cos (x) cos (2 x) + sin (x) sin (2 x)

= cos (x) cos (2 x) + sin (x) sin (2 x)

cos (x \cdot 1) - cos (x \cdot 2) = cos (x) cos (2 x) + sin (x) sin (2 x)

Simplify

cos (x \cdot 1) - cos (x \cdot 2) : cos (x) - cos (2 x)

cos (x \cdot 1) - cos (x \cdot 2)

Multiply:

x \cdot 1 = x

= cos (x) - cos (2 x)

cos (x) - cos (2 x) = cos (x) cos (2 x) + sin (x) sin (2 x)

cos (x) - cos (2 x) = cos (x) cos (2 x) + sin (x) sin (2 x)

Subtract

cos (x) cos (2 x) + sin (x) sin (2 x)

from both sides

cos (x) - cos (2 x) - cos (x) cos (2 x) - sin (x) sin (2 x) = 0

Rewrite using trig identities

- cos (2 x) + cos (x) - cos (2 x) cos (x) - sin (2 x) sin (x)

Use the Angle Difference identity:

cos (s) cos (t) + sin (s) sin (t) = cos (s - t)

- cos (s) cos (t) - sin (s) sin (t) = - cos (s - t)

= - cos (2 x) + cos (x) - cos (2 x - x)

Simplify

- cos (2 x) + cos (x) - cos (2 x - x) : - cos (2 x)

- cos (2 x) + cos (x) - cos (2 x - x)

Add similar elements:

2 x - x = x

= - cos (2 x) + cos (x) - cos (x)

Add similar elements:

cos (x) - cos (x) = 0

= - cos (2 x)

= - cos (2 x)

- cos (2 x) = 0

Divide both sides by

- 1

- cos (2 x) = 0

Divide both sides by

- 1

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

Simplify

cos (2 x) = 0

cos (2 x) = 0

General solutions for

cos (2 x) = 0

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

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

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

Solve

2 x = \frac{π}{2} + 2 πn : x = \frac{π}{4} + πn

2 x = \frac{π}{2} + 2 πn

Divide both sides by

2

2 x = \frac{π}{2} + 2 πn

Divide both sides by

2

\frac{2 x}{2} = \frac{\frac{π}{2}}{2} + \frac{2 πn}{2}

Simplify

\frac{2 x}{2} = \frac{\frac{π}{2}}{2} + \frac{2 πn}{2}

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

\frac{\frac{π}{2}}{2} + \frac{2 πn}{2} : \frac{π}{4} + πn

\frac{\frac{π}{2}}{2} + \frac{2 πn}{2}

\frac{\frac{π}{2}}{2} = \frac{π}{4}

\frac{\frac{π}{2}}{2}

Apply the fraction rule:

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

= \frac{π}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{π}{4}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

Divide the numbers:

\frac{2}{2} = 1

= πn

= \frac{π}{4} + πn

x = \frac{π}{4} + πn

x = \frac{π}{4} + πn

x = \frac{π}{4} + πn

Solve

2 x = \frac{3 π}{2} + 2 πn : x = \frac{3 π}{4} + πn

2 x = \frac{3 π}{2} + 2 πn

Divide both sides by

2

2 x = \frac{3 π}{2} + 2 πn

Divide both sides by

2

\frac{2 x}{2} = \frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2}

Simplify

\frac{2 x}{2} = \frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2}

Simplify

\frac{2 x}{2} : x

\frac{2 x}{2}

Divide the numbers:

\frac{2}{2} = 1

= x

Simplify

\frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2} : \frac{3 π}{4} + πn

\frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2}

\frac{\frac{3 π}{2}}{2} = \frac{3 π}{4}

\frac{\frac{3 π}{2}}{2}

Apply the fraction rule:

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

= \frac{3 π}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{3 π}{4}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

Divide the numbers:

\frac{2}{2} = 1

= πn

= \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

x = \frac{π}{4} + πn, x = \frac{3 π}{4} + πn

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Frequently Asked Questions (FAQ)

What is the general solution for cos(x1)-cos(x2)=cos(x1-x2) ?
The general solution for cos(x1)-cos(x2)=cos(x1-x2) is x= pi/4+pin,x=(3pi)/4+pin