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cot(x)=cot(3x-50)

解答

cot (x) = cot (3 x - 50)

解答

x = πn + 25, x = \frac{π}{2} + 25 + πn

+1

度数

x = 1432.39448 \dots^{\circ} + 18 0^{\circ} n, x = 1522.39448 \dots^{\circ} + 18 0^{\circ} n

求解步骤

cot (x) = cot (3 x - 50)

两边减去

cot (3 x - 50)

cot (x) - cot (3 x - 50) = 0

用 sin, cos 表示

- cot (- 50 + 3 x) + cot (x)

使用基本三角恒等式:

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

= - \frac{cos ( - 50 + 3 x )}{sin ( - 50 + 3 x )} + cot (x)

使用基本三角恒等式:

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

= - \frac{cos ( - 50 + 3 x )}{sin ( - 50 + 3 x )} + \frac{cos ( x )}{sin ( x )}

化简

- \frac{cos ( - 50 + 3 x )}{sin ( - 50 + 3 x )} + \frac{cos ( x )}{sin ( x )} : \frac{- cos ( - 50 + 3 x ) sin ( x ) + cos ( x ) sin ( 3 x - 50 )}{sin ( 3 x - 50 ) sin ( x )}

- \frac{cos ( - 50 + 3 x )}{sin ( - 50 + 3 x )} + \frac{cos ( x )}{sin ( x )}

sin (- 50 + 3 x), sin (x)

的最小公倍数:

sin (3 x - 50) sin (x)

sin (- 50 + 3 x), sin (x)

最小公倍数 (LCM)

计算出由出现在

sin (- 50 + 3 x)

或

sin (x)

中的因子组成的表达式

= sin (3 x - 50) sin (x)

根据最小公倍数调整分式

将每个分子乘以其分母转变为最小公倍数所要乘以的同一数值

sin (3 x - 50) sin (x)

对于

\frac{cos ( - 50 + 3 x )}{sin ( - 50 + 3 x )} :

将分母和分子乘以

sin (x)

\frac{cos ( - 50 + 3 x )}{sin ( - 50 + 3 x )} = \frac{cos ( - 50 + 3 x ) sin ( x )}{sin ( - 50 + 3 x ) sin ( x )}

对于

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

将分母和分子乘以

sin (3 x - 50)

\frac{cos ( x )}{sin ( x )} = \frac{cos ( x ) sin ( 3 x - 50 )}{sin ( x ) sin ( 3 x - 50 )}

= - \frac{cos ( - 50 + 3 x ) sin ( x )}{sin ( - 50 + 3 x ) sin ( x )} + \frac{cos ( x ) sin ( 3 x - 50 )}{sin ( x ) sin ( 3 x - 50 )}

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 ( - 50 + 3 x ) sin ( x ) + cos ( x ) sin ( 3 x - 50 )}{sin ( 3 x - 50 ) sin ( x )}

= \frac{- cos ( - 50 + 3 x ) sin ( x ) + cos ( x ) sin ( 3 x - 50 )}{sin ( 3 x - 50 ) sin ( x )}

\frac{- cos ( - 50 + 3 x ) sin ( x ) + cos ( x ) sin ( - 50 + 3 x )}{sin ( - 50 + 3 x ) sin ( x )} = 0

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

- cos (- 50 + 3 x) sin (x) + cos (x) sin (- 50 + 3 x) = 0

使用三角恒等式改写

- cos (- 50 + 3 x) sin (x) + cos (x) sin (- 50 + 3 x)

使用角差恒等式:

sin (s) cos (t) - cos (s) sin (t) = sin (s - t)

= sin (- 50 + 3 x - x)

sin (- 50 + 3 x - x) = 0

sin (- 50 + 3 x - 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}

- 50 + 3 x - x = 0 + 2 πn, - 50 + 3 x - x = π + 2 πn

- 50 + 3 x - x = 0 + 2 πn, - 50 + 3 x - x = π + 2 πn

解

- 50 + 3 x - x = 0 + 2 πn : x = πn + 25

- 50 + 3 x - x = 0 + 2 πn

同类项相加:

3 x - x = 2 x

- 50 + 2 x = 0 + 2 πn

0 + 2 πn = 2 πn

- 50 + 2 x = 2 πn

将

50

到右边

- 50 + 2 x = 2 πn

两边加上

50

- 50 + 2 x + 50 = 2 πn + 50

化简

2 x = 2 πn + 50

2 x = 2 πn + 50

两边除以

2

2 x = 2 πn + 50

两边除以

2

\frac{2 x}{2} = \frac{2 πn}{2} + \frac{50}{2}

化简

\frac{2 x}{2} = \frac{2 πn}{2} + \frac{50}{2}

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

\frac{2 πn}{2} + \frac{50}{2} : πn + 25

\frac{2 πn}{2} + \frac{50}{2}

数字相除:

\frac{2}{2} = 1

= πn + \frac{50}{2}

数字相除:

\frac{50}{2} = 25

= πn + 25

x = πn + 25

x = πn + 25

x = πn + 25

解

- 50 + 3 x - x = π + 2 πn : x = \frac{π}{2} + 25 + πn

- 50 + 3 x - x = π + 2 πn

同类项相加:

3 x - x = 2 x

- 50 + 2 x = π + 2 πn

将

50

到右边

- 50 + 2 x = π + 2 πn

两边加上

50

- 50 + 2 x + 50 = π + 2 πn + 50

化简

2 x = π + 2 πn + 50

2 x = π + 2 πn + 50

两边除以

2

2 x = π + 2 πn + 50

两边除以

2

\frac{2 x}{2} = \frac{π}{2} + \frac{2 πn}{2} + \frac{50}{2}

化简

\frac{2 x}{2} = \frac{π}{2} + \frac{2 πn}{2} + \frac{50}{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{50}{2} : \frac{π}{2} + 25 + πn

\frac{π}{2} + \frac{2 πn}{2} + \frac{50}{2}

对同类项分组

= \frac{π}{2} + \frac{50}{2} + \frac{2 πn}{2}

数字相除:

\frac{50}{2} = 25

= \frac{π}{2} + 25 + \frac{2 πn}{2}

数字相除:

\frac{2}{2} = 1

= \frac{π}{2} + 25 + πn

x = \frac{π}{2} + 25 + πn

x = \frac{π}{2} + 25 + πn

x = \frac{π}{2} + 25 + πn

x = πn + 25, x = \frac{π}{2} + 25 + πn

流行的例子

sinh (x) = - 6

tan (θ) = \frac{2}{2}

sin (θ) = \frac{33}{55}

2 cos (x) - 4 = - 3

(sin(2x)}{sin(\frac{7pi)/2-x)}=sqrt(2)

\frac{sin ( 2 x )}{sin ( \frac{7 π}{2} - x )} = 2