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受欢迎的三角函数 >

5sin(4x)=4cos(2x)

解答

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

解答

x = \frac{π + 4 πn}{4}, x = \frac{3 π + 4 πn}{4}, x = \frac{0.41151 \dots + 2 πn}{2}, x = \frac{π - 0.41151 \dots + 2 πn}{2}

+1

度数

x = 4 5^{\circ} + 18 0^{\circ} n, x = 13 5^{\circ} + 18 0^{\circ} n, x = 11.78908 \dots^{\circ} + 18 0^{\circ} n, x = 78.21091 \dots^{\circ} + 18 0^{\circ} n

求解步骤

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

两边减去

4 cos (2 x)

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

令

: u = 2 x

5 sin (2 u) - 4 cos (u) = 0

使用三角恒等式改写

- 4 cos (u) + 5 sin (2 u)

使用倍角公式:

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

= - 4 cos (u) + 5 \cdot 2 sin (u) cos (u)

化简

= - 4 cos (u) + 10 sin (u) cos (u)

- 4 cos (u) + 10 cos (u) sin (u) = 0

分解

- 4 cos (u) + 10 cos (u) sin (u) : 2 cos (u) (5 sin (u) - 2)

- 4 cos (u) + 10 cos (u) sin (u)

将

10

改写为

5 \cdot 2

将

- 4

改写为

2 \cdot 2

= 2 \cdot 2 cos (u) + 5 \cdot 2 sin (u) cos (u)

因式分解出通项

2 cos (u)

= 2 cos (u) (- 2 + 5 sin (u))

2 cos (u) (5 sin (u) - 2) = 0

分别求解每个部分

cos (u) = 0 or 5 sin (u) - 2 = 0

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

cos (u) = 0

cos (u) = 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}

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

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

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

5 sin (u) - 2 = 0

将

2

到右边

5 sin (u) - 2 = 0

两边加上

2

5 sin (u) - 2 + 2 = 0 + 2

化简

5 sin (u) = 2

5 sin (u) = 2

两边除以

5

5 sin (u) = 2

两边除以

5

\frac{5 sin ( u )}{5} = \frac{2}{5}

化简

sin (u) = \frac{2}{5}

sin (u) = \frac{2}{5}

使用反三角函数性质

sin (u) = \frac{2}{5}

sin (u) = \frac{2}{5}

的通解

sin (x) = a \Rightarrow x = arcsin (a) + 2 πn, x = π - arcsin (a) + 2 πn

u = arcsin (\frac{2}{5}) + 2 πn, u = π - arcsin (\frac{2}{5}) + 2 πn

u = arcsin (\frac{2}{5}) + 2 πn, u = π - arcsin (\frac{2}{5}) + 2 πn

合并所有解

u = \frac{π}{2} + 2 πn, u = \frac{3 π}{2} + 2 πn, u = arcsin (\frac{2}{5}) + 2 πn, u = π - arcsin (\frac{2}{5}) + 2 πn

u = 2 x

代回

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

2 x = \frac{π}{2} + 2 πn

两边除以

2

2 x = \frac{π}{2} + 2 πn

两边除以

2

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

化简

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

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

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

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

使用法则

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

= \frac{\frac{π}{2} + 2 πn}{2}

化简

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

\frac{π}{2} + 2 πn

将项转换为分式:

2 πn = \frac{2 πn 2}{2}

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

因为分母相等，所以合并分式:

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

= \frac{π + 2 πn \cdot 2}{2}

数字相乘:

2 \cdot 2 = 4

= \frac{π + 4 πn}{2}

= \frac{\frac{π + 4 πn}{2}}{2}

使用分式法则:

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

= \frac{π + 4 πn}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

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

2 x = \frac{3 π}{2} + 2 πn

两边除以

2

2 x = \frac{3 π}{2} + 2 πn

两边除以

2

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

化简

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

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

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

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

使用法则

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

= \frac{\frac{3 π}{2} + 2 πn}{2}

化简

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

\frac{3 π}{2} + 2 πn

将项转换为分式:

2 πn = \frac{2 πn 2}{2}

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

因为分母相等，所以合并分式:

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

= \frac{3 π + 2 πn \cdot 2}{2}

数字相乘:

2 \cdot 2 = 4

= \frac{3 π + 4 πn}{2}

= \frac{\frac{3 π + 4 πn}{2}}{2}

使用分式法则:

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

= \frac{3 π + 4 πn}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

2 x = arcsin (\frac{2}{5}) + 2 πn : x = \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}

2 x = arcsin (\frac{2}{5}) + 2 πn

两边除以

2

2 x = arcsin (\frac{2}{5}) + 2 πn

两边除以

2

\frac{2 x}{2} = \frac{arcsin ( \frac{2}{5} )}{2} + \frac{2 πn}{2}

化简

\frac{2 x}{2} = \frac{arcsin ( \frac{2}{5} )}{2} + \frac{2 πn}{2}

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

\frac{arcsin ( \frac{2}{5} )}{2} + \frac{2 πn}{2} : \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}

\frac{arcsin ( \frac{2}{5} )}{2} + \frac{2 πn}{2}

使用法则

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

= \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}

x = \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}

x = \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}

x = \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}

2 x = π - arcsin (\frac{2}{5}) + 2 πn : x = \frac{π - arcsin ( \frac{2}{5} ) + 2 πn}{2}

2 x = π - arcsin (\frac{2}{5}) + 2 πn

两边除以

2

2 x = π - arcsin (\frac{2}{5}) + 2 πn

两边除以

2

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

化简

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

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

\frac{π}{2} - \frac{arcsin ( \frac{2}{5} )}{2} + \frac{2 πn}{2} : \frac{π - arcsin ( \frac{2}{5} ) + 2 πn}{2}

\frac{π}{2} - \frac{arcsin ( \frac{2}{5} )}{2} + \frac{2 πn}{2}

使用法则

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

= \frac{π - arcsin ( \frac{2}{5} ) + 2 πn}{2}

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

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

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

x = \frac{π + 4 πn}{4}, x = \frac{3 π + 4 πn}{4}, x = \frac{arcsin ( \frac{2}{5} ) + 2 πn}{2}, x = \frac{π - arcsin ( \frac{2}{5} ) + 2 πn}{2}

以小数形式表示解

x = \frac{π + 4 πn}{4}, x = \frac{3 π + 4 πn}{4}, x = \frac{0.41151 \dots + 2 πn}{2}, x = \frac{π - 0.41151 \dots + 2 πn}{2}

作图

流行的例子

arccosh (x) = 1

solvefor θ,sin(3θ)= 1/2

so l v e f or θ, sin (3 θ) = \frac{1}{2}

0 = - 0.5 sin (\frac{x}{5})

(408.4)/(sin(130))=(200)/(sin(x))

\frac{408.4}{sin ( 13 0 ^{\circ} )} = \frac{200}{sin ( x )}

cot (θ) = - \frac{7}{6}