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受欢迎的三角函数 >

((1+cot^2(x)))/(cos^2(x))=cot^2(x)

解答

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

解答

x \in R 无解

求解步骤

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

两边减去

cot^{2} (x)

\frac{1 + cot ^{2} ( x )}{cos ^{2} ( x )} - cot^{2} (x) = 0

化简

\frac{1 + cot ^{2} ( x )}{cos ^{2} ( x )} - cot^{2} (x) : \frac{1 + cot ^{2} ( x ) - cot ^{2} ( x ) cos ^{2} ( x )}{cos ^{2} ( x )}

\frac{1 + cot ^{2} ( x )}{cos ^{2} ( x )} - cot^{2} (x)

将项转换为分式:

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

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

\frac{1 + cot ^{2} ( x ) - cot ^{2} ( x ) cos ^{2} ( x )}{cos ^{2} ( x )} = 0

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

1 + cot^{2} (x) - cot^{2} (x) cos^{2} (x) = 0

使用三角恒等式改写

1 + cot^{2} (x) - cos^{2} (x) cot^{2} (x)

使用毕达哥拉斯恒等式:

1 + cot^{2} (x) = csc^{2} (x)

= - cos^{2} (x) cot^{2} (x) + csc^{2} (x)

csc^{2} (x) - cos^{2} (x) cot^{2} (x) = 0

分解

csc^{2} (x) - cos^{2} (x) cot^{2} (x) : (csc (x) + cos (x) cot (x)) (csc (x) - cos (x) cot (x))

csc^{2} (x) - cos^{2} (x) cot^{2} (x)

将

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

改写为

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

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

使用指数法则:

a^{m} b^{m} = (ab)^{m}

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

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

= csc^{2} (x) - (cos (x) cot (x))^{2}

使用平方差公式:

x^{2} - y^{2} = (x + y) (x - y)

csc^{2} (x) - (cos (x) cot (x))^{2} = (csc (x) + cos (x) cot (x)) (csc (x) - cos (x) cot (x))

= (csc (x) + cos (x) cot (x)) (csc (x) - cos (x) cot (x))

(csc (x) + cos (x) cot (x)) (csc (x) - cos (x) cot (x)) = 0

分别求解每个部分

csc (x) + cos (x) cot (x) = 0 or csc (x) - cos (x) cot (x) = 0

csc (x) + cos (x) cot (x) = 0 :

无解

csc (x) + cos (x) cot (x) = 0

用 sin, cos 表示

csc (x) + cos (x) cot (x)

使用基本三角恒等式:

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

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

使用基本三角恒等式:

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

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

化简

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

\frac{1}{sin ( x )} + 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 )}

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

使用法则

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

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

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

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

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

1 + cos^{2} (x) = 0

用替代法求解

1 + cos^{2} (x) = 0

令

: cos (x) = u

1 + u^{2} = 0

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

1 + u^{2} = 0

将

1

到右边

1 + u^{2} = 0

两边减去

1

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

化简

u^{2} = - 1

u^{2} = - 1

对于

x^{2} = f (a)

解为

x = f (a), - f (a)

u = - 1, u = - - 1

化简

- 1 : i

- 1

使用虚数运算法则:

- 1 = i

= i

化简

- - 1 : - i

- - 1

使用虚数运算法则:

- 1 = i

= - i

u = i, u = - i

u = cos (x)

代回

cos (x) = i, cos (x) = - i

cos (x) = i, cos (x) = - i

cos (x) = i :

无解

cos (x) = i

无解

cos (x) = - i :

无解

cos (x) = - i

无解

合并所有解

无解

csc (x) - cos (x) cot (x) = 0 :

无解

csc (x) - cos (x) cot (x) = 0

用 sin, cos 表示

csc (x) - cos (x) cot (x)

使用基本三角恒等式:

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

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

使用基本三角恒等式:

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

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

化简

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

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

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

使用法则

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

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

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

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

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

1 - cos^{2} (x) = 0

用替代法求解

1 - cos^{2} (x) = 0

令

: cos (x) = u

1 - u^{2} = 0

1 - u^{2} = 0 : u = 1, u = - 1

1 - u^{2} = 0

将

1

到右边

1 - u^{2} = 0

两边减去

1

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

化简

- u^{2} = - 1

- u^{2} = - 1

两边除以

- 1

- u^{2} = - 1

两边除以

- 1

\frac{- u ^{2}}{- 1} = \frac{- 1}{- 1}

化简

u^{2} = 1

u^{2} = 1

对于

x^{2} = f (a)

解为

x = f (a), - f (a)

u = 1, u = - 1

1 = 1

1

使用法则

1 = 1

= 1

- 1 = - 1

- 1

使用法则

1 = 1

= - 1

u = 1, u = - 1

u = cos (x)

代回

cos (x) = 1, cos (x) = - 1

cos (x) = 1, cos (x) = - 1

cos (x) = 1 : x = 2 πn

cos (x) = 1

cos (x) = 1

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}

x = 0 + 2 πn

x = 0 + 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

cos (x) = - 1 : x = π + 2 πn

cos (x) = - 1

cos (x) = - 1

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}

x = π + 2 πn

x = π + 2 πn

合并所有解

x = 2 πn, x = π + 2 πn

因为方程对以下值无定义:

2 πn, π + 2 πn

无解

合并所有解

x \in R 无解

作图

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