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受欢迎的三角函数 >

sin(3x)=sin(5x)

解答

sin (3 x) = sin (5 x)

解答

x = \frac{π}{8} + \frac{πn}{2}, x = \frac{3 π}{8} + \frac{πn}{2}, x = 2 πn, x = π + 2 πn

+1

度数

x = 22. 5^{\circ} + 9 0^{\circ} n, x = 67. 5^{\circ} + 9 0^{\circ} n, x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n

求解步骤

sin (3 x) = sin (5 x)

两边减去

sin (5 x)

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

使用三角恒等式改写

sin (3 x) - sin (5 x)

使用和差化积恒等式:

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

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

化简

2 sin (\frac{3 x - 5 x}{2}) cos (\frac{3 x + 5 x}{2}) : - 2 cos (4 x) sin (x)

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

\frac{3 x - 5 x}{2} = - x

\frac{3 x - 5 x}{2}

同类项相加:

3 x - 5 x = - 2 x

= \frac{- 2 x}{2}

使用分式法则:

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

= - \frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= - x

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

使用负角恒等式:

sin (- x) = - sin (x)

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

去除括号:

(- a) = - a

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

\frac{3 x + 5 x}{2} = 4 x

\frac{3 x + 5 x}{2}

同类项相加:

3 x + 5 x = 8 x

= \frac{8 x}{2}

数字相除:

\frac{8}{2} = 4

= 4 x

= - 2 cos (4 x) sin (x)

= - 2 cos (4 x) sin (x)

- 2 cos (4 x) sin (x) = 0

分别求解每个部分

cos (4 x) = 0 or sin (x) = 0

cos (4 x) = 0 : x = \frac{π}{8} + \frac{πn}{2}, x = \frac{3 π}{8} + \frac{πn}{2}

cos (4 x) = 0

cos (4 x) = 0

的通解

cos (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} 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}

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

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

解

4 x = \frac{π}{2} + 2 πn : x = \frac{π}{8} + \frac{πn}{2}

4 x = \frac{π}{2} + 2 πn

两边除以

4

4 x = \frac{π}{2} + 2 πn

两边除以

4

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

化简

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

化简

\frac{4 x}{4} : x

\frac{4 x}{4}

数字相除:

\frac{4}{4} = 1

= x

化简

\frac{\frac{π}{2}}{4} + \frac{2 πn}{4} : \frac{π}{8} + \frac{πn}{2}

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

\frac{\frac{π}{2}}{4} = \frac{π}{8}

\frac{\frac{π}{2}}{4}

使用分式法则:

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

= \frac{π}{2 \cdot 4}

数字相乘:

2 \cdot 4 = 8

= \frac{π}{8}

\frac{2 πn}{4} = \frac{πn}{2}

\frac{2 πn}{4}

约分:

2

= \frac{πn}{2}

= \frac{π}{8} + \frac{πn}{2}

x = \frac{π}{8} + \frac{πn}{2}

x = \frac{π}{8} + \frac{πn}{2}

x = \frac{π}{8} + \frac{πn}{2}

解

4 x = \frac{3 π}{2} + 2 πn : x = \frac{3 π}{8} + \frac{πn}{2}

4 x = \frac{3 π}{2} + 2 πn

两边除以

4

4 x = \frac{3 π}{2} + 2 πn

两边除以

4

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

化简

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

化简

\frac{4 x}{4} : x

\frac{4 x}{4}

数字相除:

\frac{4}{4} = 1

= x

化简

\frac{\frac{3 π}{2}}{4} + \frac{2 πn}{4} : \frac{3 π}{8} + \frac{πn}{2}

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

\frac{\frac{3 π}{2}}{4} = \frac{3 π}{8}

\frac{\frac{3 π}{2}}{4}

使用分式法则:

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

= \frac{3 π}{2 \cdot 4}

数字相乘:

2 \cdot 4 = 8

= \frac{3 π}{8}

\frac{2 πn}{4} = \frac{πn}{2}

\frac{2 πn}{4}

约分:

2

= \frac{πn}{2}

= \frac{3 π}{8} + \frac{πn}{2}

x = \frac{3 π}{8} + \frac{πn}{2}

x = \frac{3 π}{8} + \frac{πn}{2}

x = \frac{3 π}{8} + \frac{πn}{2}

x = \frac{π}{8} + \frac{πn}{2}, x = \frac{3 π}{8} + \frac{πn}{2}

sin (x) = 0 : x = 2 πn, x = π + 2 πn

sin (x) = 0

sin (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}

x = 0 + 2 πn, x = π + 2 πn

x = 0 + 2 πn, x = π + 2 πn

解

x = 0 + 2 πn : x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn, x = π + 2 πn

合并所有解

x = \frac{π}{8} + \frac{πn}{2}, x = \frac{3 π}{8} + \frac{πn}{2}, x = 2 πn, x = π + 2 πn

作图

流行的例子

2sin^2(3θ)+sin(3θ)-1=0

2 sin^{2} (3 θ) + sin (3 θ) - 1 = 0

4cos(θ)+sqrt(3)=2cos(θ)

4 cos (θ) + 3 = 2 cos (θ)

6cos^2(θ)-cos(θ)-1=0

6 cos^{2} (θ) - cos (θ) - 1 = 0

∣ cos (3 x) ∣ = \frac{1}{2}

solvefor g,θ(t)=-1cos(sqrt(g/l)t)

so l v e f or g, θ (t) = - 1 cos (\frac{g}{l} t)