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受欢迎的三角函数 >

(cos(x)*cot(x))/(1-sin(x))=3

解答

\frac{cos ( x ) \cdot cot ( x )}{1 - sin ( x )} = 3

解答

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

+1

度数

x = 3 0^{\circ} + 36 0^{\circ} n, x = 15 0^{\circ} + 36 0^{\circ} n

求解步骤

\frac{cos ( x ) cot ( x )}{1 - sin ( x )} = 3

两边减去

3

\frac{cos ( x ) cot ( x )}{1 - sin ( x )} - 3 = 0

化简

\frac{cos ( x ) cot ( x )}{1 - sin ( x )} - 3 : \frac{cos ( x ) cot ( x ) - 3 ( 1 - sin ( x ) )}{1 - sin ( x )}

\frac{cos ( x ) cot ( x )}{1 - sin ( x )} - 3

将项转换为分式:

3 = \frac{3 ( 1 - sin ( x ) )}{1 - sin ( x )}

= \frac{cos ( x ) cot ( x )}{1 - sin ( x )} - \frac{3 ( 1 - sin ( x ) )}{1 - sin ( x )}

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{cos ( x ) cot ( x ) - 3 ( 1 - sin ( x ) )}{1 - sin ( x )}

\frac{cos ( x ) cot ( x ) - 3 ( 1 - sin ( x ) )}{1 - sin ( x )} = 0

\frac{f ( x )}{g ( x )} = 0 \Rightarrow f (x) = 0

cos (x) cot (x) - 3 (1 - sin (x)) = 0

使用三角恒等式改写

- (1 - sin (x)) \cdot 3 + cos (x) cot (x)

使用基本三角恒等式:

cot (x) = \frac{cos ( x )}{sin ( x )}

= - (1 - sin (x)) \cdot 3 + cos (x) \frac{cos ( x )}{sin ( x )}

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

cos (x) \frac{cos ( x )}{sin ( x )}

分式相乘:

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

= \frac{cos ( x ) cos ( x )}{sin ( x )}

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

cos (x) cos (x)

使用指数法则:

a^{b} \cdot a^{c} = a^{b + c}

cos (x) cos (x) = cos^{1 + 1} (x)

= cos^{1 + 1} (x)

数字相加:

1 + 1 = 2

= cos^{2} (x)

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

= - 3 (1 - sin (x)) + \frac{cos ^{2} ( x )}{sin ( x )}

使用毕达哥拉斯恒等式:

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

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

= \frac{1 - sin ^{2} ( x )}{sin ( x )} - (1 - sin (x)) \cdot 3

化简

\frac{1 - sin ^{2} ( x )}{sin ( x )} - (1 - sin (x)) \cdot 3 : \frac{1 + 2 sin ^{2} ( x )}{sin ( x )} - 3

\frac{1 - sin ^{2} ( x )}{sin ( x )} - (1 - sin (x)) \cdot 3

= \frac{1 - sin ^{2} ( x )}{sin ( x )} - 3 (1 - sin (x))

乘开

- 3 (1 - sin (x)) : - 3 + 3 sin (x)

- 3 (1 - sin (x))

使用分配律:

a (b - c) = ab - a c

a = - 3, b = 1, c = sin (x)

= - 3 \cdot 1 - (- 3) sin (x)

使用加减运算法则

- (- a) = a

= - 3 \cdot 1 + 3 sin (x)

数字相乘:

3 \cdot 1 = 3

= - 3 + 3 sin (x)

= \frac{1 - sin ^{2} ( x )}{sin ( x )} - 3 + 3 sin (x)

合并分式

\frac{- sin ^{2} ( x ) + 1}{sin ( x )} + 3 sin (x) : \frac{1 + 2 sin ^{2} ( x )}{sin ( x )}

\frac{- sin ^{2} ( x ) + 1}{sin ( x )} + 3 sin (x)

将项转换为分式:

3 sin (x) = \frac{3 sin ( x ) sin ( x )}{sin ( x )}

= \frac{1 - sin ^{2} ( x )}{sin ( x )} + \frac{3 sin ( x ) sin ( x )}{sin ( x )}

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{1 - sin ^{2} ( x ) + 3 sin ( x ) sin ( x )}{sin ( x )}

1 - sin^{2} (x) + 3 sin (x) sin (x) = 1 + 2 sin^{2} (x)

1 - sin^{2} (x) + 3 sin (x) sin (x)

3 sin (x) sin (x) = 3 sin^{2} (x)

3 sin (x) sin (x)

使用指数法则:

a^{b} \cdot a^{c} = a^{b + c}

sin (x) sin (x) = sin^{1 + 1} (x)

= 3 sin^{1 + 1} (x)

数字相加:

1 + 1 = 2

= 3 sin^{2} (x)

= 1 - sin^{2} (x) + 3 sin^{2} (x)

同类项相加:

- sin^{2} (x) + 3 sin^{2} (x) = 2 sin^{2} (x)

= 1 + 2 sin^{2} (x)

= \frac{1 + 2 sin ^{2} ( x )}{sin ( x )}

= \frac{2 sin ^{2} ( x ) + 1}{sin ( x )} - 3

= \frac{1 + 2 sin ^{2} ( x )}{sin ( x )} - 3

- 3 + \frac{1 + 2 sin ^{2} ( x )}{sin ( x )} = 0

用替代法求解

- 3 + \frac{1 + 2 sin ^{2} ( x )}{sin ( x )} = 0

令

: sin (x) = u

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

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

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

在两边乘以

u

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

在两边乘以

u

- 3 u + \frac{1 + 2 u ^{2}}{u} u = 0 \cdot u

化简

- 3 u + \frac{1 + 2 u ^{2}}{u} u = 0 \cdot u

化简

\frac{1 + 2 u ^{2}}{u} u : 1 + 2 u^{2}

\frac{1 + 2 u ^{2}}{u} u

分式相乘:

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

= \frac{( 1 + 2 u ^{2} ) u}{u}

约分:

u

= 1 + 2 u^{2}

化简

0 \cdot u : 0

0 \cdot u

使用法则

0 \cdot a = 0

= 0

- 3 u + 1 + 2 u^{2} = 0

- 3 u + 1 + 2 u^{2} = 0

- 3 u + 1 + 2 u^{2} = 0

解

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

- 3 u + 1 + 2 u^{2} = 0

改写成标准形式

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

2 u^{2} - 3 u + 1 = 0

使用求根公式求解

2 u^{2} - 3 u + 1 = 0

二次方程求根公式:

若

a = 2, b = - 3, c = 1

u_{1, 2} = \frac{- ( - 3 ) \pm ( - 3 ) ^{2} - 4 \cdot 2 \cdot 1}{2 \cdot 2}

u_{1, 2} = \frac{- ( - 3 ) \pm ( - 3 ) ^{2} - 4 \cdot 2 \cdot 1}{2 \cdot 2}

(- 3)^{2} - 4 \cdot 2 \cdot 1 = 1

(- 3)^{2} - 4 \cdot 2 \cdot 1

使用指数法则:

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

若

n

是偶数

(- 3)^{2} = 3^{2}

= 3^{2} - 4 \cdot 2 \cdot 1

数字相乘:

4 \cdot 2 \cdot 1 = 8

= 3^{2} - 8

3^{2} = 9

= 9 - 8

数字相减:

9 - 8 = 1

= 1

使用法则

1 = 1

= 1

u_{1, 2} = \frac{- ( - 3 ) \pm 1}{2 \cdot 2}

将解分隔开

u_{1} = \frac{- ( - 3 ) + 1}{2 \cdot 2}, u_{2} = \frac{- ( - 3 ) - 1}{2 \cdot 2}

u = \frac{- ( - 3 ) + 1}{2 \cdot 2} : 1

\frac{- ( - 3 ) + 1}{2 \cdot 2}

使用法则

- (- a) = a

= \frac{3 + 1}{2 \cdot 2}

数字相加:

3 + 1 = 4

= \frac{4}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{4}{4}

使用法则

\frac{a}{a} = 1

= 1

u = \frac{- ( - 3 ) - 1}{2 \cdot 2} : \frac{1}{2}

\frac{- ( - 3 ) - 1}{2 \cdot 2}

使用法则

- (- a) = a

= \frac{3 - 1}{2 \cdot 2}

数字相减:

3 - 1 = 2

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

数字相乘:

2 \cdot 2 = 4

= \frac{2}{4}

约分:

2

= \frac{1}{2}

二次方程组的解是:

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

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

验证解

找到无定义的点（奇点）:

u = 0

取

- 3 + \frac{1 + 2 u ^{2}}{u}

的分母，令其等于零

u = 0

以下点无定义

u = 0

将不在定义域的点与解相综合:

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

u = sin (x)

代回

sin (x) = 1, sin (x) = \frac{1}{2}

sin (x) = 1, sin (x) = \frac{1}{2}

sin (x) = 1 : x = \frac{π}{2} + 2 πn

sin (x) = 1

sin (x) = 1

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 = \frac{π}{2} + 2 πn

x = \frac{π}{2} + 2 πn

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

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

sin (x) = \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}

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

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

合并所有解

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

因为方程对以下值无定义:

\frac{π}{2} + 2 πn

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

作图

流行的例子

(sin(8))/(30)=(sin(θ))/(120)

\frac{sin ( 8 )}{30} = \frac{sin ( θ )}{120}

114 = sin (x)

cos(θ)=(11.14)/(13)

cos (θ) = \frac{11.14}{13}

cos (t) = 0.5

cos(2θ)(4sin^2(θ)+1)=0

cos (2 θ) (4 sin^{2} (θ) + 1) = 0