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(1+cos(4x))sin(4x)=cos^2(2x)

解答

(1 + cos (4 x)) sin (4 x) = cos^{2} (2 x)

解答

x = \frac{π}{4} + πn, x = \frac{3 π}{4} + πn, x = \frac{π}{24} + \frac{πn}{2}, x = \frac{5 π}{24} + \frac{πn}{2}

+1

度数

x = 4 5^{\circ} + 18 0^{\circ} n, x = 13 5^{\circ} + 18 0^{\circ} n, x = 7. 5^{\circ} + 9 0^{\circ} n, x = 37. 5^{\circ} + 9 0^{\circ} n

求解步骤

(1 + cos (4 x)) sin (4 x) = cos^{2} (2 x)

两边减去

cos^{2} (2 x)

sin (4 x) (1 + cos (4 x)) - cos^{2} (2 x) = 0

使用三角恒等式改写

- cos^{2} (2 x) + (1 + cos (4 x)) sin (4 x)

cos (4 x) = 2 cos^{2} (2 x) - 1

cos (4 x)

改写为

= cos (2 \cdot 2 x)

使用倍角公式:

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

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

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

= - cos^{2} (2 x) + sin (4 x) (1 + 2 cos^{2} (2 x) - 1)

化简

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

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

对同类项分组

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

1 - 1 = 0

= 2 cos^{2} (2 x)

= - cos^{2} (2 x) + 2 cos^{2} (2 x) sin (4 x)

- cos^{2} (2 x) + 2 cos^{2} (2 x) sin (4 x) = 0

分解

- cos^{2} (2 x) + 2 cos^{2} (2 x) sin (4 x) : cos^{2} (2 x) (2 sin (4 x) - 1)

- cos^{2} (2 x) + 2 cos^{2} (2 x) sin (4 x)

因式分解出通项

cos^{2} (2 x)

= cos^{2} (2 x) (- 1 + 2 sin (4 x))

cos^{2} (2 x) (2 sin (4 x) - 1) = 0

分别求解每个部分

cos^{2} (2 x) = 0 or 2 sin (4 x) - 1 = 0

cos^{2} (2 x) = 0 : x = \frac{π}{4} + πn, x = \frac{3 π}{4} + πn

cos^{2} (2 x) = 0

使用法则

x^{n} = 0 \Rightarrow x = 0

cos (2 x) = 0

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

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

解

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

2 x = \frac{π}{2} + 2 πn

两边除以

2

2 x = \frac{π}{2} + 2 πn

两边除以

2

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

化简

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

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

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

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

\frac{\frac{π}{2}}{2} = \frac{π}{4}

\frac{\frac{π}{2}}{2}

使用分式法则:

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

= \frac{π}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{π}{4}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

数字相除:

\frac{2}{2} = 1

= πn

= \frac{π}{4} + πn

x = \frac{π}{4} + πn

x = \frac{π}{4} + πn

x = \frac{π}{4} + πn

解

2 x = \frac{3 π}{2} + 2 πn : x = \frac{3 π}{4} + πn

2 x = \frac{3 π}{2} + 2 πn

两边除以

2

2 x = \frac{3 π}{2} + 2 πn

两边除以

2

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

化简

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

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

\frac{\frac{3 π}{2}}{2} + \frac{2 πn}{2} : \frac{3 π}{4} + πn

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

\frac{\frac{3 π}{2}}{2} = \frac{3 π}{4}

\frac{\frac{3 π}{2}}{2}

使用分式法则:

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

= \frac{3 π}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{3 π}{4}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

数字相除:

\frac{2}{2} = 1

= πn

= \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

x = \frac{π}{4} + πn, x = \frac{3 π}{4} + πn

2 sin (4 x) - 1 = 0 : x = \frac{π}{24} + \frac{πn}{2}, x = \frac{5 π}{24} + \frac{πn}{2}

2 sin (4 x) - 1 = 0

将

1

到右边

2 sin (4 x) - 1 = 0

两边加上

1

2 sin (4 x) - 1 + 1 = 0 + 1

化简

2 sin (4 x) = 1

2 sin (4 x) = 1

两边除以

2

2 sin (4 x) = 1

两边除以

2

\frac{2 sin ( 4 x )}{2} = \frac{1}{2}

化简

sin (4 x) = \frac{1}{2}

sin (4 x) = \frac{1}{2}

sin (4 x) = \frac{1}{2}

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}

4 x = \frac{π}{6} + 2 πn, 4 x = \frac{5 π}{6} + 2 πn

4 x = \frac{π}{6} + 2 πn, 4 x = \frac{5 π}{6} + 2 πn

解

4 x = \frac{π}{6} + 2 πn : x = \frac{π}{24} + \frac{πn}{2}

4 x = \frac{π}{6} + 2 πn

两边除以

4

4 x = \frac{π}{6} + 2 πn

两边除以

4

\frac{4 x}{4} = \frac{\frac{π}{6}}{4} + \frac{2 πn}{4}

化简

\frac{4 x}{4} = \frac{\frac{π}{6}}{4} + \frac{2 πn}{4}

化简

\frac{4 x}{4} : x

\frac{4 x}{4}

数字相除:

\frac{4}{4} = 1

= x

化简

\frac{\frac{π}{6}}{4} + \frac{2 πn}{4} : \frac{π}{24} + \frac{πn}{2}

\frac{\frac{π}{6}}{4} + \frac{2 πn}{4}

\frac{\frac{π}{6}}{4} = \frac{π}{24}

\frac{\frac{π}{6}}{4}

使用分式法则:

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

= \frac{π}{6 \cdot 4}

数字相乘:

6 \cdot 4 = 24

= \frac{π}{24}

\frac{2 πn}{4} = \frac{πn}{2}

\frac{2 πn}{4}

约分:

2

= \frac{πn}{2}

= \frac{π}{24} + \frac{πn}{2}

x = \frac{π}{24} + \frac{πn}{2}

x = \frac{π}{24} + \frac{πn}{2}

x = \frac{π}{24} + \frac{πn}{2}

解

4 x = \frac{5 π}{6} + 2 πn : x = \frac{5 π}{24} + \frac{πn}{2}

4 x = \frac{5 π}{6} + 2 πn

两边除以

4

4 x = \frac{5 π}{6} + 2 πn

两边除以

4

\frac{4 x}{4} = \frac{\frac{5 π}{6}}{4} + \frac{2 πn}{4}

化简

\frac{4 x}{4} = \frac{\frac{5 π}{6}}{4} + \frac{2 πn}{4}

化简

\frac{4 x}{4} : x

\frac{4 x}{4}

数字相除:

\frac{4}{4} = 1

= x

化简

\frac{\frac{5 π}{6}}{4} + \frac{2 πn}{4} : \frac{5 π}{24} + \frac{πn}{2}

\frac{\frac{5 π}{6}}{4} + \frac{2 πn}{4}

\frac{\frac{5 π}{6}}{4} = \frac{5 π}{24}

\frac{\frac{5 π}{6}}{4}

使用分式法则:

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

= \frac{5 π}{6 \cdot 4}

数字相乘:

6 \cdot 4 = 24

= \frac{5 π}{24}

\frac{2 πn}{4} = \frac{πn}{2}

\frac{2 πn}{4}

约分:

2

= \frac{πn}{2}

= \frac{5 π}{24} + \frac{πn}{2}

x = \frac{5 π}{24} + \frac{πn}{2}

x = \frac{5 π}{24} + \frac{πn}{2}

x = \frac{5 π}{24} + \frac{πn}{2}

x = \frac{π}{24} + \frac{πn}{2}, x = \frac{5 π}{24} + \frac{πn}{2}

合并所有解

x = \frac{π}{4} + πn, x = \frac{3 π}{4} + πn, x = \frac{π}{24} + \frac{πn}{2}, x = \frac{5 π}{24} + \frac{πn}{2}

流行的例子

arcsin(3/5)+arccos(x)=pi

arcsin (\frac{3}{5}) + arccos (x) = π

cos (θ) = \frac{6}{7}

2cos(2θ)+7sin(θ)=5

2 cos (2 θ) + 7 sin (θ) = 5

tan (x^{2}) = 1

cos (x) = \frac{5}{10}