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受欢迎的三角函数 >

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

解答

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

解答

x = \frac{π + 12 πn}{12}, x = \frac{5 π + 12 πn}{12}, x = πn, x = \frac{π + 2 πn}{2}

+1

度数

x = 1 5^{\circ} + 18 0^{\circ} n, x = 7 5^{\circ} + 18 0^{\circ} n, x = 0^{\circ} + 18 0^{\circ} n, x = 9 0^{\circ} + 18 0^{\circ} n

求解步骤

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

两边减去

sin (2 x)

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

令

: u = 2 x

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

使用三角恒等式改写

1 - cos (2 u) - sin (u)

使用倍角公式:

cos (2 x) = 1 - 2 sin^{2} (x)

= 1 - (1 - 2 sin^{2} (u)) - sin (u)

化简

1 - (1 - 2 sin^{2} (u)) - sin (u) : 2 sin^{2} (u) - sin (u)

1 - (1 - 2 sin^{2} (u)) - sin (u)

- (1 - 2 sin^{2} (u)) : - 1 + 2 sin^{2} (u)

- (1 - 2 sin^{2} (u))

打开括号

= - (1) - (- 2 sin^{2} (u))

使用加减运算法则

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

= - 1 + 2 sin^{2} (u)

= 1 - 1 + 2 sin^{2} (u) - sin (u)

1 - 1 = 0

= 2 sin^{2} (u) - sin (u)

= 2 sin^{2} (u) - sin (u)

- sin (u) + 2 sin^{2} (u) = 0

用替代法求解

- sin (u) + 2 sin^{2} (u) = 0

令

: sin (u) = u

- u + 2 u^{2} = 0

- u + 2 u^{2} = 0 : u = \frac{1}{2}, u = 0

- u + 2 u^{2} = 0

改写成标准形式

a x^{2} + b x + c = 0

2 u^{2} - u = 0

使用求根公式求解

2 u^{2} - u = 0

二次方程求根公式:

若

a = 2, b = - 1, c = 0

u_{1, 2} = \frac{- ( - 1 ) \pm ( - 1 ) ^{2} - 4 \cdot 2 \cdot 0}{2 \cdot 2}

u_{1, 2} = \frac{- ( - 1 ) \pm ( - 1 ) ^{2} - 4 \cdot 2 \cdot 0}{2 \cdot 2}

(- 1)^{2} - 4 \cdot 2 \cdot 0 = 1

(- 1)^{2} - 4 \cdot 2 \cdot 0

(- 1)^{2} = 1

(- 1)^{2}

使用指数法则:

(- a)^{n} = a^{n},

若

n

是偶数

(- 1)^{2} = 1^{2}

= 1^{2}

使用法则

1^{a} = 1

= 1

4 \cdot 2 \cdot 0 = 0

4 \cdot 2 \cdot 0

使用法则

0 \cdot a = 0

= 0

= 1 - 0

数字相减:

1 - 0 = 1

= 1

使用法则

1 = 1

= 1

u_{1, 2} = \frac{- ( - 1 ) \pm 1}{2 \cdot 2}

将解分隔开

u_{1} = \frac{- ( - 1 ) + 1}{2 \cdot 2}, u_{2} = \frac{- ( - 1 ) - 1}{2 \cdot 2}

u = \frac{- ( - 1 ) + 1}{2 \cdot 2} : \frac{1}{2}

\frac{- ( - 1 ) + 1}{2 \cdot 2}

使用法则

- (- a) = a

= \frac{1 + 1}{2 \cdot 2}

数字相加:

1 + 1 = 2

= \frac{2}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{2}{4}

约分:

2

= \frac{1}{2}

u = \frac{- ( - 1 ) - 1}{2 \cdot 2} : 0

\frac{- ( - 1 ) - 1}{2 \cdot 2}

使用法则

- (- a) = a

= \frac{1 - 1}{2 \cdot 2}

数字相减:

1 - 1 = 0

= \frac{0}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{0}{4}

使用法则

\frac{0}{a} = 0, a \neq = 0

= 0

二次方程组的解是:

u = \frac{1}{2}, u = 0

u = sin (u)

代回

sin (u) = \frac{1}{2}, sin (u) = 0

sin (u) = \frac{1}{2}, sin (u) = 0

sin (u) = \frac{1}{2} : u = \frac{π}{6} + 2 πn, u = \frac{5 π}{6} + 2 πn

sin (u) = \frac{1}{2}

sin (u) = \frac{1}{2}

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}

u = \frac{π}{6} + 2 πn, u = \frac{5 π}{6} + 2 πn

u = \frac{π}{6} + 2 πn, u = \frac{5 π}{6} + 2 πn

sin (u) = 0 : u = 2 πn, u = π + 2 πn

sin (u) = 0

sin (u) = 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}

u = 0 + 2 πn, u = π + 2 πn

u = 0 + 2 πn, u = π + 2 πn

解

u = 0 + 2 πn : u = 2 πn

u = 0 + 2 πn

0 + 2 πn = 2 πn

u = 2 πn

u = 2 πn, u = π + 2 πn

合并所有解

u = \frac{π}{6} + 2 πn, u = \frac{5 π}{6} + 2 πn, u = 2 πn, u = π + 2 πn

u = 2 x

代回

2 x = \frac{π}{6} + 2 πn : x = \frac{π + 12 πn}{12}

2 x = \frac{π}{6} + 2 πn

两边除以

2

2 x = \frac{π}{6} + 2 πn

两边除以

2

\frac{2 x}{2} = \frac{\frac{π}{6}}{2} + \frac{2 πn}{2}

化简

\frac{2 x}{2} = \frac{\frac{π}{6}}{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}{6}}{2} + \frac{2 πn}{2} : \frac{π + 12 πn}{12}

\frac{\frac{π}{6}}{2} + \frac{2 πn}{2}

使用法则

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

= \frac{\frac{π}{6} + 2 πn}{2}

化简

\frac{π}{6} + 2 πn : \frac{π + 12 πn}{6}

\frac{π}{6} + 2 πn

将项转换为分式:

2 πn = \frac{2 πn 6}{6}

= \frac{π}{6} + \frac{2 πn \cdot 6}{6}

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 6}{6}

数字相乘:

2 \cdot 6 = 12

= \frac{π + 12 πn}{6}

= \frac{\frac{π + 12 πn}{6}}{2}

使用分式法则:

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

= \frac{π + 12 πn}{6 \cdot 2}

数字相乘:

6 \cdot 2 = 12

= \frac{π + 12 πn}{12}

x = \frac{π + 12 πn}{12}

x = \frac{π + 12 πn}{12}

x = \frac{π + 12 πn}{12}

2 x = \frac{5 π}{6} + 2 πn : x = \frac{5 π + 12 πn}{12}

2 x = \frac{5 π}{6} + 2 πn

两边除以

2

2 x = \frac{5 π}{6} + 2 πn

两边除以

2

\frac{2 x}{2} = \frac{\frac{5 π}{6}}{2} + \frac{2 πn}{2}

化简

\frac{2 x}{2} = \frac{\frac{5 π}{6}}{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{5 π}{6}}{2} + \frac{2 πn}{2} : \frac{5 π + 12 πn}{12}

\frac{\frac{5 π}{6}}{2} + \frac{2 πn}{2}

使用法则

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

= \frac{\frac{5 π}{6} + 2 πn}{2}

化简

\frac{5 π}{6} + 2 πn : \frac{5 π + 12 πn}{6}

\frac{5 π}{6} + 2 πn

将项转换为分式:

2 πn = \frac{2 πn 6}{6}

= \frac{5 π}{6} + \frac{2 πn \cdot 6}{6}

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{5 π + 2 πn \cdot 6}{6}

数字相乘:

2 \cdot 6 = 12

= \frac{5 π + 12 πn}{6}

= \frac{\frac{5 π + 12 πn}{6}}{2}

使用分式法则:

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

= \frac{5 π + 12 πn}{6 \cdot 2}

数字相乘:

6 \cdot 2 = 12

= \frac{5 π + 12 πn}{12}

x = \frac{5 π + 12 πn}{12}

x = \frac{5 π + 12 πn}{12}

x = \frac{5 π + 12 πn}{12}

2 x = 2 πn : x = πn

2 x = 2 πn

两边除以

2

2 x = 2 πn

两边除以

2

\frac{2 x}{2} = \frac{2 πn}{2}

化简

x = πn

x = πn

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

2 x = π + 2 πn

两边除以

2

2 x = π + 2 πn

两边除以

2

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

化简

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

\frac{π}{2} + \frac{2 πn}{2}

使用法则

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

= \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 12 πn}{12}, x = \frac{5 π + 12 πn}{12}, x = πn, x = \frac{π + 2 πn}{2}

作图

流行的例子

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

cos (2 x) = sin^{2} (x)

sec^2(x)-3tan(x)=5

sec^{2} (x) - 3 tan (x) = 5

sin (x) = 0, 4

sin (x) = 0, 2

sin (u) = 0.8746