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受欢迎的三角函数 >

2sin(6x)+2sin(2x)=0

解答

2 sin (6 x) + 2 sin (2 x) = 0

解答

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

+1

度数

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

求解步骤

2 sin (6 x) + 2 sin (2 x) = 0

令

: u = 2 x

2 sin (3 u) + 2 sin (u) = 0

使用三角恒等式改写

2 sin (3 u) + 2 sin (u)

sin (3 u) = 3 sin (u) - 4 sin^{3} (u)

sin (3 u)

使用三角恒等式改写

sin (3 u)

改写为

= sin (2 u + u)

使用角和恒等式:

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

= sin (2 u) cos (u) + cos (2 u) sin (u)

使用倍角公式:

sin (2 u) = 2 sin (u) cos (u)

= cos (2 u) sin (u) + cos (u) 2 sin (u) cos (u)

化简

cos (2 u) sin (u) + cos (u) \cdot 2 sin (u) cos (u) : sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

cos (2 u) sin (u) + cos (u) 2 sin (u) cos (u)

cos (u) \cdot 2 sin (u) cos (u) = 2 cos^{2} (u) sin (u)

cos (u) 2 sin (u) cos (u)

使用指数法则:

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

cos (u) cos (u) = cos^{1 + 1} (u)

= 2 sin (u) cos^{1 + 1} (u)

数字相加:

1 + 1 = 2

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

= sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

= sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

= sin (u) cos (2 u) + 2 cos^{2} (u) sin (u)

使用倍角公式:

cos (2 u) = 1 - 2 sin^{2} (u)

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

使用毕达哥拉斯恒等式:

cos^{2} (u) + sin^{2} (u) = 1

cos^{2} (u) = 1 - sin^{2} (u)

= (1 - 2 sin^{2} (u)) sin (u) + 2 (1 - sin^{2} (u)) sin (u)

乘开

(1 - 2 sin^{2} (u)) sin (u) + 2 (1 - sin^{2} (u)) sin (u) : - 4 sin^{3} (u) + 3 sin (u)

(1 - 2 sin^{2} (u)) sin (u) + 2 (1 - sin^{2} (u)) sin (u)

= sin (u) (1 - 2 sin^{2} (u)) + 2 sin (u) (1 - sin^{2} (u))

乘开

sin (u) (1 - 2 sin^{2} (u)) : sin (u) - 2 sin^{3} (u)

sin (u) (1 - 2 sin^{2} (u))

使用分配律:

a (b - c) = ab - a c

a = sin (u), b = 1, c = 2 sin^{2} (u)

= sin (u) 1 - sin (u) 2 sin^{2} (u)

= 1 sin (u) - 2 sin^{2} (u) sin (u)

化简

1 \cdot sin (u) - 2 sin^{2} (u) sin (u) : sin (u) - 2 sin^{3} (u)

1 sin (u) - 2 sin^{2} (u) sin (u)

1 \cdot sin (u) = sin (u)

1 sin (u)

乘以:

1 \cdot sin (u) = sin (u)

= sin (u)

2 sin^{2} (u) sin (u) = 2 sin^{3} (u)

2 sin^{2} (u) sin (u)

使用指数法则:

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

sin^{2} (u) sin (u) = sin^{2 + 1} (u)

= 2 sin^{2 + 1} (u)

数字相加:

2 + 1 = 3

= 2 sin^{3} (u)

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

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

= sin (u) - 2 sin^{3} (u) + 2 (1 - sin^{2} (u)) sin (u)

乘开

2 sin (u) (1 - sin^{2} (u)) : 2 sin (u) - 2 sin^{3} (u)

2 sin (u) (1 - sin^{2} (u))

使用分配律:

a (b - c) = ab - a c

a = 2 sin (u), b = 1, c = sin^{2} (u)

= 2 sin (u) 1 - 2 sin (u) sin^{2} (u)

= 2 \cdot 1 sin (u) - 2 sin^{2} (u) sin (u)

化简

2 \cdot 1 \cdot sin (u) - 2 sin^{2} (u) sin (u) : 2 sin (u) - 2 sin^{3} (u)

2 \cdot 1 sin (u) - 2 sin^{2} (u) sin (u)

2 \cdot 1 \cdot sin (u) = 2 sin (u)

2 \cdot 1 sin (u)

数字相乘:

2 \cdot 1 = 2

= 2 sin (u)

2 sin^{2} (u) sin (u) = 2 sin^{3} (u)

2 sin^{2} (u) sin (u)

使用指数法则:

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

sin^{2} (u) sin (u) = sin^{2 + 1} (u)

= 2 sin^{2 + 1} (u)

数字相加:

2 + 1 = 3

= 2 sin^{3} (u)

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

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

= sin (u) - 2 sin^{3} (u) + 2 sin (u) - 2 sin^{3} (u)

化简

sin (u) - 2 sin^{3} (u) + 2 sin (u) - 2 sin^{3} (u) : - 4 sin^{3} (u) + 3 sin (u)

sin (u) - 2 sin^{3} (u) + 2 sin (u) - 2 sin^{3} (u)

对同类项分组

= - 2 sin^{3} (u) - 2 sin^{3} (u) + sin (u) + 2 sin (u)

同类项相加:

- 2 sin^{3} (u) - 2 sin^{3} (u) = - 4 sin^{3} (u)

= - 4 sin^{3} (u) + sin (u) + 2 sin (u)

同类项相加:

sin (u) + 2 sin (u) = 3 sin (u)

= - 4 sin^{3} (u) + 3 sin (u)

= - 4 sin^{3} (u) + 3 sin (u)

= - 4 sin^{3} (u) + 3 sin (u)

= 2 (3 sin (u) - 4 sin^{3} (u)) + 2 sin (u)

化简

2 (3 sin (u) - 4 sin^{3} (u)) + 2 sin (u) : 8 sin (u) - 8 sin^{3} (u)

2 (3 sin (u) - 4 sin^{3} (u)) + 2 sin (u)

乘开

2 (3 sin (u) - 4 sin^{3} (u)) : 6 sin (u) - 8 sin^{3} (u)

2 (3 sin (u) - 4 sin^{3} (u))

使用分配律:

a (b - c) = ab - a c

a = 2, b = 3 sin (u), c = 4 sin^{3} (u)

= 2 \cdot 3 sin (u) - 2 \cdot 4 sin^{3} (u)

化简

2 \cdot 3 sin (u) - 2 \cdot 4 sin^{3} (u) : 6 sin (u) - 8 sin^{3} (u)

2 \cdot 3 sin (u) - 2 \cdot 4 sin^{3} (u)

数字相乘:

2 \cdot 3 = 6

= 6 sin (u) - 2 \cdot 4 sin^{3} (u)

数字相乘:

2 \cdot 4 = 8

= 6 sin (u) - 8 sin^{3} (u)

= 6 sin (u) - 8 sin^{3} (u)

= 6 sin (u) - 8 sin^{3} (u) + 2 sin (u)

同类项相加:

6 sin (u) + 2 sin (u) = 8 sin (u)

= 8 sin (u) - 8 sin^{3} (u)

= 8 sin (u) - 8 sin^{3} (u)

8 sin (u) - 8 sin^{3} (u) = 0

用替代法求解

8 sin (u) - 8 sin^{3} (u) = 0

令

: sin (u) = u

8 u - 8 u^{3} = 0

8 u - 8 u^{3} = 0 : u = 0, u = - 1, u = 1

8 u - 8 u^{3} = 0

因式分解

8 u - 8 u^{3} : - 8 u (u + 1) (u - 1)

8 u - 8 u^{3}

因式分解出通项

- 8 u : - 8 u (u^{2} - 1)

- 8 u^{3} + 8 u

使用指数法则:

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

u^{3} = u^{2} u

= - 8 u^{2} u + 8 u

因式分解出通项

- 8 u

= - 8 u (u^{2} - 1)

= - 8 u (u^{2} - 1)

分解

u^{2} - 1 : (u + 1) (u - 1)

u^{2} - 1

将

1

改写为

1^{2}

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

使用平方差公式:

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

u^{2} - 1^{2} = (u + 1) (u - 1)

= (u + 1) (u - 1)

= - 8 u (u + 1) (u - 1)

- 8 u (u + 1) (u - 1) = 0

使用零因数法则： If

ab = 0

then

a = 0

or

b = 0

u = 0 or u + 1 = 0 or u - 1 = 0

解

u + 1 = 0 : u = - 1

u + 1 = 0

将

1

到右边

u + 1 = 0

两边减去

1

u + 1 - 1 = 0 - 1

化简

u = - 1

u = - 1

解

u - 1 = 0 : u = 1

u - 1 = 0

将

1

到右边

u - 1 = 0

两边加上

1

u - 1 + 1 = 0 + 1

化简

u = 1

u = 1

解为

u = 0, u = - 1, u = 1

u = sin (u)

代回

sin (u) = 0, sin (u) = - 1, sin (u) = 1

sin (u) = 0, sin (u) = - 1, sin (u) = 1

sin (u) = 0 : u = 2 πn, u = π + 2 πn

sin (u) = 0

sin (u) = 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}

u = 0 + 2 πn, u = π + 2 πn

u = 0 + 2 πn, u = π + 2 πn

解

u = 0 + 2 πn : u = 2 πn

u = 0 + 2 πn

0 + 2 πn = 2 πn

u = 2 πn

u = 2 πn, u = π + 2 πn

sin (u) = - 1 : u = \frac{3 π}{2} + 2 πn

sin (u) = - 1

sin (u) = - 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}

u = \frac{3 π}{2} + 2 πn

u = \frac{3 π}{2} + 2 πn

sin (u) = 1 : u = \frac{π}{2} + 2 πn

sin (u) = 1

sin (u) = 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}

u = \frac{π}{2} + 2 πn

u = \frac{π}{2} + 2 πn

合并所有解

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

u = 2 x

代回

2 x = 2 πn : x = πn

2 x = 2 πn

两边除以

2

2 x = 2 πn

两边除以

2

\frac{2 x}{2} = \frac{2 πn}{2}

化简

x = πn

x = πn

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

2 x = π + 2 πn

两边除以

2

2 x = π + 2 πn

两边除以

2

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

化简

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

\frac{π}{2} + \frac{2 πn}{2}

使用法则

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

= \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

x = \frac{π + 2 πn}{2}

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

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}{4}

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

使用法则

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

= \frac{\frac{3 π}{2} + 2 πn}{2}

化简

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

\frac{3 π}{2} + 2 πn

将项转换为分式:

2 πn = \frac{2 πn 2}{2}

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

数字相乘:

2 \cdot 2 = 4

= \frac{3 π + 4 πn}{2}

= \frac{\frac{3 π + 4 πn}{2}}{2}

使用分式法则:

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

= \frac{3 π + 4 πn}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

x = \frac{3 π + 4 πn}{4}

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

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}{4}

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

使用法则

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

= \frac{\frac{π}{2} + 2 πn}{2}

化简

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

\frac{π}{2} + 2 πn

将项转换为分式:

2 πn = \frac{2 πn 2}{2}

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

数字相乘:

2 \cdot 2 = 4

= \frac{π + 4 πn}{2}

= \frac{\frac{π + 4 πn}{2}}{2}

使用分式法则:

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

= \frac{π + 4 πn}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

x = \frac{π + 4 πn}{4}

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

作图

流行的例子

tan^2(2x)-1=sec(2x)

tan^{2} (2 x) - 1 = sec (2 x)

- 1.92 = cos (x)

5cot^2(x)+8cot(x)+3=0

5 cot^{2} (x) + 8 cot (x) + 3 = 0

sin (x) = \frac{15}{31}

4 cot (θ) - 1 = 0