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tan(2x)=cot(x)

解答

tan (2 x) = cot (x)

解答

x = \frac{π}{6} + \frac{2 πn}{3}, x = \frac{π}{2} + \frac{2 πn}{3}

+1

度数

x = 3 0^{\circ} + 12 0^{\circ} n, x = 9 0^{\circ} + 12 0^{\circ} n

求解步骤

tan (2 x) = cot (x)

两边减去

cot (x)

tan (2 x) - cot (x) = 0

用 sin, cos 表示

- cot (x) + tan (2 x)

使用基本三角恒等式:

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

= - \frac{cos ( x )}{sin ( x )} + tan (2 x)

使用基本三角恒等式:

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

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

化简

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

- \frac{cos ( x )}{sin ( x )} + \frac{sin ( 2 x )}{cos ( 2 x )}

sin (x), cos (2 x)

的最小公倍数:

sin (x) cos (2 x)

sin (x), cos (2 x)

最小公倍数 (LCM)

计算出由出现在

sin (x)

或

cos (2 x)

中的因子组成的表达式

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

对于

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

将分母和分子乘以

cos (2 x)

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

对于

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

将分母和分子乘以

sin (x)

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

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

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

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

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

- cos (2 x) cos (x) + sin (2 x) sin (x) = 0

使用三角恒等式改写

- cos (2 x) cos (x) + sin (2 x) sin (x)

使用角和恒等式:

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

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

= - cos (2 x + x)

- cos (2 x + x) = 0

两边除以

- 1

- cos (2 x + x) = 0

两边除以

- 1

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

化简

cos (2 x + x) = 0

cos (2 x + x) = 0

cos (2 x + 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}

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

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

解

2 x + x = \frac{π}{2} + 2 πn : x = \frac{π}{6} + \frac{2 πn}{3}

2 x + x = \frac{π}{2} + 2 πn

同类项相加:

2 x + x = 3 x

3 x = \frac{π}{2} + 2 πn

两边除以

3

3 x = \frac{π}{2} + 2 πn

两边除以

3

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

化简

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

化简

\frac{3 x}{3} : x

\frac{3 x}{3}

数字相除:

\frac{3}{3} = 1

= x

化简

\frac{\frac{π}{2}}{3} + \frac{2 πn}{3} : \frac{π}{6} + \frac{2 πn}{3}

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

\frac{\frac{π}{2}}{3} = \frac{π}{6}

\frac{\frac{π}{2}}{3}

使用分式法则:

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

= \frac{π}{2 \cdot 3}

数字相乘:

2 \cdot 3 = 6

= \frac{π}{6}

= \frac{π}{6} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}

解

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

2 x + x = \frac{3 π}{2} + 2 πn

同类项相加:

2 x + x = 3 x

3 x = \frac{3 π}{2} + 2 πn

两边除以

3

3 x = \frac{3 π}{2} + 2 πn

两边除以

3

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

化简

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

化简

\frac{3 x}{3} : x

\frac{3 x}{3}

数字相除:

\frac{3}{3} = 1

= x

化简

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

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

\frac{\frac{3 π}{2}}{3} = \frac{π}{2}

\frac{\frac{3 π}{2}}{3}

使用分式法则:

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

= \frac{3 π}{2 \cdot 3}

数字相乘:

2 \cdot 3 = 6

= \frac{3 π}{6}

约分:

3

= \frac{π}{2}

= \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}, x = \frac{π}{2} + \frac{2 πn}{3}

流行的例子

cos (x) = 0.7

2-2cos^2(x)=sin(x)+1

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

sin (x) = - \frac{1}{4}

sin(x)+cos(2x)=0

sin (x) + cos (2 x) = 0

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

sin (x) - cos (x) = 2