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受欢迎的三角函数 >

3/(cos^2(x))=(7+4)/(cot(x))

解答

\frac{3}{cos ^{2} ( x )} = \frac{7 + 4}{cot ( x )}

解答

x = \frac{0.57693 \dots}{2} + πn, x = \frac{π}{2} - \frac{0.57693 \dots}{2} + πn

+1

度数

x = 16.52786 \dots^{\circ} + 18 0^{\circ} n, x = 73.47213 \dots^{\circ} + 18 0^{\circ} n

求解步骤

\frac{3}{cos ^{2} ( x )} = \frac{7 + 4}{cot ( x )}

两边减去

\frac{7 + 4}{cot ( x )}

\frac{3}{cos ^{2} ( x )} - \frac{11}{cot ( x )} = 0

化简

\frac{3}{cos ^{2} ( x )} - \frac{11}{cot ( x )} : \frac{3 cot ( x ) - 11 cos ^{2} ( x )}{cos ^{2} ( x ) cot ( x )}

\frac{3}{cos ^{2} ( x )} - \frac{11}{cot ( x )}

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

的最小公倍数:

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

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

最小公倍数 (LCM)

计算出由出现在

cos^{2} (x)

或

cot (x)

中的因子组成的表达式

= cos^{2} (x) cot (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

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

对于

\frac{3}{cos ^{2} ( x )} :

将分母和分子乘以

cot (x)

\frac{3}{cos ^{2} ( x )} = \frac{3 cot ( x )}{cos ^{2} ( x ) cot ( x )}

对于

\frac{11}{cot ( x )} :

将分母和分子乘以

cos^{2} (x)

\frac{11}{cot ( x )} = \frac{11 cos ^{2} ( x )}{cot ( x ) cos ^{2} ( x )}

= \frac{3 cot ( x )}{cos ^{2} ( x ) cot ( x )} - \frac{11 cos ^{2} ( x )}{cot ( 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{3 cot ( x ) - 11 cos ^{2} ( x )}{cos ^{2} ( x ) cot ( x )}

\frac{3 cot ( x ) - 11 cos ^{2} ( x )}{cos ^{2} ( x ) cot ( x )} = 0

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

3 cot (x) - 11 cos^{2} (x) = 0

用 sin, cos 表示

- 11 cos^{2} (x) + 3 cot (x)

使用基本三角恒等式:

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

= - 11 cos^{2} (x) + 3 \cdot \frac{cos ( x )}{sin ( x )}

化简

- 11 cos^{2} (x) + 3 \cdot \frac{cos ( x )}{sin ( x )} : \frac{- 11 cos ^{2} ( x ) sin ( x ) + 3 cos ( x )}{sin ( x )}

- 11 cos^{2} (x) + 3 \cdot \frac{cos ( x )}{sin ( x )}

乘

3 \cdot \frac{cos ( x )}{sin ( x )} : \frac{3 cos ( x )}{sin ( x )}

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

分式相乘:

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

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

= - 11 cos^{2} (x) + \frac{3 cos ( x )}{sin ( x )}

将项转换为分式:

11 cos^{2} (x) = \frac{11 cos ^{2} ( x ) sin ( x )}{sin ( x )}

= - \frac{11 cos ^{2} ( x ) sin ( x )}{sin ( x )} + \frac{cos ( x ) \cdot 3}{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{- 11 cos ^{2} ( x ) sin ( x ) + cos ( x ) \cdot 3}{sin ( x )}

= \frac{- 11 cos ^{2} ( x ) sin ( x ) + 3 cos ( x )}{sin ( x )}

\frac{3 cos ( x ) - 11 cos ^{2} ( x ) sin ( x )}{sin ( x )} = 0

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

3 cos (x) - 11 cos^{2} (x) sin (x) = 0

分解

3 cos (x) - 11 cos^{2} (x) sin (x) : cos (x) (3 - 11 sin (x) cos (x))

3 cos (x) - 11 cos^{2} (x) sin (x)

使用指数法则:

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

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

= 3 cos (x) - 11 cos (x) cos (x)

因式分解出通项

cos (x)

= cos (x) (3 - 11 sin (x) cos (x))

cos (x) (3 - 11 sin (x) cos (x)) = 0

分别求解每个部分

cos (x) = 0 or 3 - 11 sin (x) cos (x) = 0

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

cos (x) = 0

cos (x) = 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}

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

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

3 - 11 sin (x) cos (x) = 0 : x = \frac{arcsin ( \frac{6}{11} )}{2} + πn, x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

3 - 11 sin (x) cos (x) = 0

使用三角恒等式改写

3 - 11 sin (x) cos (x)

使用倍角公式:

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

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

= 3 - 11 \cdot \frac{sin ( 2 x )}{2}

3 - 11 \cdot \frac{sin ( 2 x )}{2} = 0

将

3

到右边

3 - 11 \cdot \frac{sin ( 2 x )}{2} = 0

两边减去

3

3 - 11 \cdot \frac{sin ( 2 x )}{2} - 3 = 0 - 3

化简

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

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

整理

- 11 \cdot \frac{sin ( 2 x )}{2} : - \frac{11 sin ( 2 x )}{2}

- 11 \cdot \frac{sin ( 2 x )}{2}

分式相乘:

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

= - \frac{sin ( 2 x ) \cdot 11}{2}

- \frac{11 sin ( 2 x )}{2} = - 3

在两边乘以

2

- \frac{11 sin ( 2 x )}{2} = - 3

在两边乘以

2

- \frac{11 sin ( 2 x )}{2} \cdot 2 = - 3 \cdot 2

化简

- \frac{11 sin ( 2 x )}{2} \cdot 2 = - 3 \cdot 2

化简

- \frac{11 sin ( 2 x )}{2} \cdot 2 : - 11 sin (2 x)

- \frac{11 sin ( 2 x )}{2} \cdot 2

分式相乘:

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

= - \frac{11 sin ( 2 x ) \cdot 2}{2}

约分:

2

= - 11 sin (2 x)

化简

- 3 \cdot 2 : - 6

- 3 \cdot 2

数字相乘:

3 \cdot 2 = 6

= - 6

- 11 sin (2 x) = - 6

- 11 sin (2 x) = - 6

- 11 sin (2 x) = - 6

两边除以

- 11

- 11 sin (2 x) = - 6

两边除以

- 11

\frac{- 11 sin ( 2 x )}{- 11} = \frac{- 6}{- 11}

化简

sin (2 x) = \frac{6}{11}

sin (2 x) = \frac{6}{11}

使用反三角函数性质

sin (2 x) = \frac{6}{11}

sin (2 x) = \frac{6}{11}

的通解

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

2 x = arcsin (\frac{6}{11}) + 2 πn, 2 x = π - arcsin (\frac{6}{11}) + 2 πn

2 x = arcsin (\frac{6}{11}) + 2 πn, 2 x = π - arcsin (\frac{6}{11}) + 2 πn

解

2 x = arcsin (\frac{6}{11}) + 2 πn : x = \frac{arcsin ( \frac{6}{11} )}{2} + πn

2 x = arcsin (\frac{6}{11}) + 2 πn

两边除以

2

2 x = arcsin (\frac{6}{11}) + 2 πn

两边除以

2

\frac{2 x}{2} = \frac{arcsin ( \frac{6}{11} )}{2} + \frac{2 πn}{2}

化简

x = \frac{arcsin ( \frac{6}{11} )}{2} + πn

x = \frac{arcsin ( \frac{6}{11} )}{2} + πn

解

2 x = π - arcsin (\frac{6}{11}) + 2 πn : x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

2 x = π - arcsin (\frac{6}{11}) + 2 πn

两边除以

2

2 x = π - arcsin (\frac{6}{11}) + 2 πn

两边除以

2

\frac{2 x}{2} = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + \frac{2 πn}{2}

化简

x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

x = \frac{arcsin ( \frac{6}{11} )}{2} + πn, x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

合并所有解

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn, x = \frac{arcsin ( \frac{6}{11} )}{2} + πn, x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

因为方程对以下值无定义:

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

x = \frac{arcsin ( \frac{6}{11} )}{2} + πn, x = \frac{π}{2} - \frac{arcsin ( \frac{6}{11} )}{2} + πn

以小数形式表示解

x = \frac{0.57693 \dots}{2} + πn, x = \frac{π}{2} - \frac{0.57693 \dots}{2} + πn

作图

流行的例子

sin (x) = 0.01

sin(x)-sin(2x)=sin^3(x)

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

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

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

sin(x)= 4/5 , pi/2 <= 0<pi,sin(2x)

sin (x) = \frac{4}{5}, \frac{π}{2} \leq 0 < π, sin (2 x)

2cos^2(θ)-3cos(θ)+1=0,(3pi)/2 <θ<2pi

2 cos^{2} (θ) - 3 cos (θ) + 1 = 0, \frac{3 π}{2} < θ < 2 π