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受欢迎的三角函数 >

0=-cos(8x)+cos(2x)

解答

0 = - cos (8 x) + cos (2 x)

解答

x = \frac{2 πn}{3}, x = \frac{π}{3} + \frac{2 πn}{3}, x = \frac{2 πn}{5}, x = \frac{π}{5} + \frac{2 πn}{5}

+1

度数

x = 0^{\circ} + 12 0^{\circ} n, x = 6 0^{\circ} + 12 0^{\circ} n, x = 0^{\circ} + 7 2^{\circ} n, x = 3 6^{\circ} + 7 2^{\circ} n

求解步骤

0 = - cos (8 x) + cos (2 x)

交换两边

- cos (8 x) + cos (2 x) = 0

使用三角恒等式改写

cos (2 x) - cos (8 x)

使用和差化积恒等式:

cos (s) - cos (t) = - 2 sin (\frac{s + t}{2}) sin (\frac{s - t}{2})

= - 2 sin (\frac{2 x + 8 x}{2}) sin (\frac{2 x - 8 x}{2})

化简

- 2 sin (\frac{2 x + 8 x}{2}) sin (\frac{2 x - 8 x}{2}) : 2 sin (3 x) sin (5 x)

- 2 sin (\frac{2 x + 8 x}{2}) sin (\frac{2 x - 8 x}{2})

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

\frac{2 x + 8 x}{2}

同类项相加:

2 x + 8 x = 10 x

= \frac{10 x}{2}

数字相除:

\frac{10}{2} = 5

= 5 x

= - 2 sin (5 x) sin (\frac{2 x - 8 x}{2})

\frac{2 x - 8 x}{2} = - 3 x

\frac{2 x - 8 x}{2}

同类项相加:

2 x - 8 x = - 6 x

= \frac{- 6 x}{2}

使用分式法则:

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

= - \frac{6 x}{2}

数字相除:

\frac{6}{2} = 3

= - 3 x

= - 2 sin (5 x) sin (- 3 x)

使用负角恒等式:

sin (- x) = - sin (x)

= - 2 (- sin (3 x)) sin (5 x)

使用法则

- (- a) = a

= 2 sin (3 x) sin (5 x)

= 2 sin (3 x) sin (5 x)

2 sin (3 x) sin (5 x) = 0

分别求解每个部分

sin (3 x) = 0 or sin (5 x) = 0

sin (3 x) = 0 : x = \frac{2 πn}{3}, x = \frac{π}{3} + \frac{2 πn}{3}

sin (3 x) = 0

sin (3 x) = 0

的通解

sin (x)

周期表（周期为

2 πn

"）：

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}

3 x = 0 + 2 πn, 3 x = π + 2 πn

3 x = 0 + 2 πn, 3 x = π + 2 πn

解

3 x = 0 + 2 πn : x = \frac{2 πn}{3}

3 x = 0 + 2 πn

0 + 2 πn = 2 πn

3 x = 2 πn

两边除以

3

3 x = 2 πn

两边除以

3

\frac{3 x}{3} = \frac{2 πn}{3}

化简

x = \frac{2 πn}{3}

x = \frac{2 πn}{3}

解

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

3 x = π + 2 πn

两边除以

3

3 x = π + 2 πn

两边除以

3

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

化简

x = \frac{π}{3} + \frac{2 πn}{3}

x = \frac{π}{3} + \frac{2 πn}{3}

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

sin (5 x) = 0 : x = \frac{2 πn}{5}, x = \frac{π}{5} + \frac{2 πn}{5}

sin (5 x) = 0

sin (5 x) = 0

的通解

sin (x)

周期表（周期为

2 πn

"）：

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}

5 x = 0 + 2 πn, 5 x = π + 2 πn

5 x = 0 + 2 πn, 5 x = π + 2 πn

解

5 x = 0 + 2 πn : x = \frac{2 πn}{5}

5 x = 0 + 2 πn

0 + 2 πn = 2 πn

5 x = 2 πn

两边除以

5

5 x = 2 πn

两边除以

5

\frac{5 x}{5} = \frac{2 πn}{5}

化简

x = \frac{2 πn}{5}

x = \frac{2 πn}{5}

解

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

5 x = π + 2 πn

两边除以

5

5 x = π + 2 πn

两边除以

5

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

化简

x = \frac{π}{5} + \frac{2 πn}{5}

x = \frac{π}{5} + \frac{2 πn}{5}

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

合并所有解

x = \frac{2 πn}{3}, x = \frac{π}{3} + \frac{2 πn}{3}, x = \frac{2 πn}{5}, x = \frac{π}{5} + \frac{2 πn}{5}

作图

流行的例子

tan (x) = \frac{3}{6}

tan(x)+tan(x+45)=-2

tan (x) + tan (x + 4 5^{\circ}) = - 2

tan(x)=(22.5)/(34)

tan (x) = \frac{22.5}{34}

tan^{2} (4 x) = 0

tan(x-45)-tan(x+45)=4

tan (x - 4 5^{\circ}) - tan (x + 4 5^{\circ}) = 4