What is the general solution for sin(7x)=cos(2x) ?

The general solution for sin(7x)=cos(2x) is x=(pi+4pin)/(18),x=(pi+4pin)/(10)

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sin(7x)=cos(2x)

Solution

sin (7 x) = cos (2 x)

Solution

x = \frac{π + 4 πn}{18}, x = \frac{π + 4 πn}{10}

Degrees

x = 1 0^{\circ} + 4 0^{\circ} n, x = 1 8^{\circ} + 7 2^{\circ} n

Solution steps

sin (7 x) = cos (2 x)

Rewrite using trig identities

sin (7 x) = cos (2 x)

Use the following identity:

cos (x) = sin (\frac{π}{2} - x)

sin (7 x) = sin (\frac{π}{2} - 2 x)

sin (7 x) = sin (\frac{π}{2} - 2 x)

Apply trig inverse properties

sin (7 x) = sin (\frac{π}{2} - 2 x)

sin (x) = sin (y) \Rightarrow x = y + 2 π n, x = π - y + 2 π n

7 x = \frac{π}{2} - 2 x + 2 πn, 7 x = π - (\frac{π}{2} - 2 x) + 2 πn

7 x = \frac{π}{2} - 2 x + 2 πn, 7 x = π - (\frac{π}{2} - 2 x) + 2 πn

7 x = \frac{π}{2} - 2 x + 2 πn : x = \frac{π + 4 πn}{18}

7 x = \frac{π}{2} - 2 x + 2 πn

Move

2 x

to the left side

7 x = \frac{π}{2} - 2 x + 2 πn

Add

2 x

to both sides

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

Simplify

9 x = \frac{π}{2} + 2 πn

9 x = \frac{π}{2} + 2 πn

Divide both sides by

9

9 x = \frac{π}{2} + 2 πn

Divide both sides by

9

\frac{9 x}{9} = \frac{\frac{π}{2}}{9} + \frac{2 πn}{9}

Simplify

\frac{9 x}{9} = \frac{\frac{π}{2}}{9} + \frac{2 πn}{9}

Simplify

\frac{9 x}{9} : x

\frac{9 x}{9}

Divide the numbers:

\frac{9}{9} = 1

= x

Simplify

\frac{\frac{π}{2}}{9} + \frac{2 πn}{9} : \frac{π + 4 πn}{18}

\frac{\frac{π}{2}}{9} + \frac{2 πn}{9}

Apply rule

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

= \frac{\frac{π}{2} + 2 πn}{9}

Join

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

\frac{π}{2} + 2 πn

Convert element to fraction:

2 πn = \frac{2 πn 2}{2}

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

Since the denominators are equal, combine the fractions:

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

= \frac{π + 2 πn \cdot 2}{2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{π + 4 πn}{2}

= \frac{\frac{π + 4 πn}{2}}{9}

Apply the fraction rule:

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

= \frac{π + 4 πn}{2 \cdot 9}

Multiply the numbers:

2 \cdot 9 = 18

= \frac{π + 4 πn}{18}

x = \frac{π + 4 πn}{18}

x = \frac{π + 4 πn}{18}

x = \frac{π + 4 πn}{18}

7 x = π - (\frac{π}{2} - 2 x) + 2 πn : x = \frac{π + 4 πn}{10}

7 x = π - (\frac{π}{2} - 2 x) + 2 πn

Expand

π - (\frac{π}{2} - 2 x) + 2 πn : π - \frac{π}{2} + 2 x + 2 πn

π - (\frac{π}{2} - 2 x) + 2 πn

- (\frac{π}{2} - 2 x) : - \frac{π}{2} + 2 x

- (\frac{π}{2} - 2 x)

Distribute parentheses

= - (\frac{π}{2}) - (- 2 x)

Apply minus-plus rules

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

= - \frac{π}{2} + 2 x

= π - \frac{π}{2} + 2 x + 2 πn

7 x = π - \frac{π}{2} + 2 x + 2 πn

Move

2 x

to the left side

7 x = π - \frac{π}{2} + 2 x + 2 πn

Subtract

2 x

from both sides

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

Simplify

5 x = π - \frac{π}{2} + 2 πn

5 x = π - \frac{π}{2} + 2 πn

Divide both sides by

5

5 x = π - \frac{π}{2} + 2 πn

Divide both sides by

5

\frac{5 x}{5} = \frac{π}{5} - \frac{\frac{π}{2}}{5} + \frac{2 πn}{5}

Simplify

\frac{5 x}{5} = \frac{π}{5} - \frac{\frac{π}{2}}{5} + \frac{2 πn}{5}

Simplify

\frac{5 x}{5} : x

\frac{5 x}{5}

Divide the numbers:

\frac{5}{5} = 1

= x

Simplify

\frac{π}{5} - \frac{\frac{π}{2}}{5} + \frac{2 πn}{5} : \frac{π + 4 πn}{10}

\frac{π}{5} - \frac{\frac{π}{2}}{5} + \frac{2 πn}{5}

Apply rule

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

= \frac{π - \frac{π}{2} + 2 πn}{5}

Join

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

π - \frac{π}{2} + 2 πn

Convert element to fraction:

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

= \frac{π 2}{2} - \frac{π}{2} + \frac{2 πn \cdot 2}{2}

Since the denominators are equal, combine the fractions:

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

= \frac{π 2 - π + 2 πn \cdot 2}{2}

π 2 - π + 2 πn \cdot 2 = π + 4 πn

π 2 - π + 2 πn \cdot 2

Add similar elements:

2 π - π = π

= π + 2 \cdot 2 πn

Multiply the numbers:

2 \cdot 2 = 4

= π + 4 πn

= \frac{π + 4 πn}{2}

= \frac{\frac{π + 4 πn}{2}}{5}

Apply the fraction rule:

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

= \frac{π + 4 πn}{2 \cdot 5}

Multiply the numbers:

2 \cdot 5 = 10

= \frac{π + 4 πn}{10}

x = \frac{π + 4 πn}{10}

x = \frac{π + 4 πn}{10}

x = \frac{π + 4 πn}{10}

x = \frac{π + 4 πn}{18}, x = \frac{π + 4 πn}{10}

x = \frac{π + 4 πn}{18}, x = \frac{π + 4 πn}{10}

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Frequently Asked Questions (FAQ)

What is the general solution for sin(7x)=cos(2x) ?
The general solution for sin(7x)=cos(2x) is x=(pi+4pin)/(18),x=(pi+4pin)/(10)