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受欢迎的三角函数 >

tan(x/2)+cos(x)=1

解答

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

解答

x = \frac{π}{2} + 2 πn, x = 4 πn, x = 2 π + 4 πn

+1

度数

x = 9 0^{\circ} + 36 0^{\circ} n, x = 0^{\circ} + 72 0^{\circ} n, x = 36 0^{\circ} + 72 0^{\circ} n

求解步骤

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

两边减去

1

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

用 sin, cos 表示

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

使用基本三角恒等式:

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

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

化简

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

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

将项转换为分式:

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

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

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

乘以:

1 \cdot cos (\frac{x}{2}) = cos (\frac{x}{2})

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

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

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

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

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

使用三角恒等式改写

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

使用积化和差恒等式:

cos (s) cos (t) = \frac{1}{2} (cos (s - t) + cos (s + t))

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

化简

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

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

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

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

分式相乘:

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

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

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

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

乘以:

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

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

去除括号:

(a) = a

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

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

化简

\frac{x}{2} - x : - \frac{x}{2}

\frac{x}{2} - x

将项转换为分式:

x = \frac{x 2}{2}

= \frac{x}{2} - \frac{x \cdot 2}{2}

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{x - x \cdot 2}{2}

同类项相加:

x - 2 x = - x

= \frac{- x}{2}

使用分式法则:

\frac{- a}{b} = - \frac{a}{b}

= - \frac{x}{2}

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

化简

\frac{x}{2} + x : \frac{3 x}{2}

\frac{x}{2} + x

将项转换为分式:

x = \frac{x 2}{2}

= \frac{x}{2} + \frac{x \cdot 2}{2}

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{x + x \cdot 2}{2}

同类项相加:

x + 2 x = 3 x

= \frac{3 x}{2}

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

化简

cos (- \frac{x}{2}) + cos (\frac{3 x}{2}) : cos (\frac{x}{2}) + cos (\frac{3 x}{2})

cos (- \frac{x}{2}) + cos (\frac{3 x}{2})

使用负角恒等式:

cos (- x) = cos (x)

= cos (\frac{x}{2}) + cos (\frac{3 x}{2})

= \frac{cos ( \frac{x}{2} ) + cos ( \frac{3 x}{2} )}{2}

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

将项转换为分式:

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

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

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

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

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

对同类项分组

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

同类项相加:

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

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

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

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

使用和差化积恒等式:

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

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

化简

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

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

合并分式

\frac{3 x}{2} - \frac{x}{2} : x

使用法则

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

= \frac{3 x - x}{2}

同类项相加:

3 x - x = 2 x

= \frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

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

合并分式

\frac{3 x}{2} + \frac{x}{2} : 2 x

使用法则

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

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

同类项相加:

3 x + x = 4 x

= \frac{4 x}{2}

数字相除:

\frac{4}{2} = 2

= 2 x

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

分解

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

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

改写为

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

因式分解出通项

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

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

整理后得

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

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

数字相除:

\frac{2}{2} = 1

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

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

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

分别求解每个部分

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

1 - sin (x) = 0 : x = \frac{π}{2} + 2 πn

1 - sin (x) = 0

将

1

到右边

1 - sin (x) = 0

两边减去

1

1 - sin (x) - 1 = 0 - 1

化简

- sin (x) = - 1

- sin (x) = - 1

两边除以

- 1

- sin (x) = - 1

两边除以

- 1

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

化简

sin (x) = 1

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 (\frac{x}{2}) = 0 : x = 4 πn, x = 2 π + 4 πn

sin (\frac{x}{2}) = 0

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

\frac{x}{2} = 0 + 2 πn, \frac{x}{2} = π + 2 πn

\frac{x}{2} = 0 + 2 πn, \frac{x}{2} = π + 2 πn

解

\frac{x}{2} = 0 + 2 πn : x = 4 πn

\frac{x}{2} = 0 + 2 πn

0 + 2 πn = 2 πn

\frac{x}{2} = 2 πn

在两边乘以

2

\frac{x}{2} = 2 πn

在两边乘以

2

\frac{2 x}{2} = 2 \cdot 2 πn

化简

x = 4 πn

x = 4 πn

解

\frac{x}{2} = π + 2 πn : x = 2 π + 4 πn

\frac{x}{2} = π + 2 πn

在两边乘以

2

\frac{x}{2} = π + 2 πn

在两边乘以

2

\frac{2 x}{2} = 2 π + 2 \cdot 2 πn

化简

x = 2 π + 4 πn

x = 2 π + 4 πn

x = 4 πn, x = 2 π + 4 πn

合并所有解

x = \frac{π}{2} + 2 πn, x = 4 πn, x = 2 π + 4 πn

作图

流行的例子

sinh (z) = - 1

1+cos^2(a)=2cos^2(a)

1 + cos^{2} (a) = 2 cos^{2} (a)

sin (x) = \frac{15}{18}

cos(5x)=cos(5+x)

cos (5 x) = cos (5 + x)

6cos^2(x)-7cos(x)-5=0

6 cos^{2} (x) - 7 cos (x) - 5 = 0