zs

English

Español

Português

Français

Deutsch

Italiano

Русский

中文(简体)

한국어

日本語

Tiếng Việt

עברית

العربية

受欢迎的三角函数 >

sin(x)sin(2x)=sin(3x)

解答

sin (x) sin (2 x) = sin (3 x)

解答

x = 2 πn, x = π + 2 πn, x = \frac{π}{4} + πn, x = - 1.24904 \dots + πn

+1

度数

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = 4 5^{\circ} + 18 0^{\circ} n, x = - 71.56505 \dots^{\circ} + 18 0^{\circ} n

求解步骤

sin (x) sin (2 x) = sin (3 x)

两边减去

sin (3 x)

sin (x) sin (2 x) - sin (3 x) = 0

使用三角恒等式改写

- sin (3 x) + sin (2 x) sin (x)

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

sin (3 x)

使用三角恒等式改写

sin (3 x)

改写为

= sin (2 x + x)

使用角和恒等式:

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

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

使用倍角公式:

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

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

使用倍角公式:

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

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

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

乘开

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

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

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

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

使用指数法则:

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

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

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

数字相加:

1 + 1 = 2

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

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

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

乘开

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

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

使用分配律:

a (b - c) = ab - a c

a = sin (x), b = cos^{2} (x), c = sin^{2} (x)

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

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

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

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

使用指数法则:

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

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

= sin^{2 + 1} (x)

数字相加:

2 + 1 = 3

= sin^{3} (x)

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

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

化简

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

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

对同类项分组

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

同类项相加:

cos^{2} (x) sin (x) + 2 cos^{2} (x) sin (x) = 3 cos^{2} (x) sin (x)

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

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

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

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

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

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

打开括号

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

使用加减运算法则

- (- a) = a, - (a) = - a

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

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

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

分解

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

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

使用指数法则:

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

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

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

因式分解出通项

sin (x)

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

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

分别求解每个部分

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

sin (x) = 0 : x = 2 πn, x = π + 2 πn

sin (x) = 0

sin (x) = 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}

x = 0 + 2 πn, x = π + 2 πn

x = 0 + 2 πn, x = π + 2 πn

解

x = 0 + 2 πn : x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn, x = π + 2 πn

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

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

使用三角恒等式改写

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

使用倍角公式:

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

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

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

分解

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

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

将表达式拆分成组

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

定义

3

的因数:

1, 3

3

约数 (因数)

找到

3

的质因数:

3

3

3

是质数，因此无法因数分解

= 3

加 1

1

3

的因数

1, 3

3

的负因数:

- 1, - 3

将因数乘以

- 1

得到负因数

- 1, - 3

对于每两个因数

u * v = - 3

，检验是否

u + v = 2

检验

u = 1, v = - 3 : u * v = - 3, u + v = - 2 \Rightarrow

假检验

u = 3, v = - 1 : u * v = - 3, u + v = 2 \Rightarrow

真

u = 3, v = - 1

分组为

(a x^{2} + ux y) + (vx y + c y^{2})

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

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

从

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

分解出因式

sin (x)

:

sin (x) (sin (x) - cos (x))

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

使用指数法则:

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

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

= sin (x) sin (x) - sin (x) cos (x)

因式分解出通项

sin (x)

= sin (x) (sin (x) - cos (x))

从

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

分解出因式

3 cos (x)

:

3 cos (x) (sin (x) - cos (x))

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

使用指数法则:

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

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

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

因式分解出通项

3 cos (x)

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

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

因式分解出通项

sin (x) - cos (x)

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

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

分别求解每个部分

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

sin (x) - cos (x) = 0 : x = \frac{π}{4} + πn

sin (x) - cos (x) = 0

使用三角恒等式改写

sin (x) - cos (x) = 0

在两边除以

cos (x), cos (x) \neq = 0

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

化简

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

使用基本三角恒等式:

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

tan (x) - 1 = 0

tan (x) - 1 = 0

将

1

到右边

tan (x) - 1 = 0

两边加上

1

tan (x) - 1 + 1 = 0 + 1

化简

tan (x) = 1

tan (x) = 1

tan (x) = 1

的通解

tan (x)

周期表（周期为

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} tan (x) 0 \frac{3}{3} 13 \pm \infty - 3 - 1 - \frac{3}{3}

x = \frac{π}{4} + πn

x = \frac{π}{4} + πn

sin (x) + 3 cos (x) = 0 : x = arctan (- 3) + πn

sin (x) + 3 cos (x) = 0

使用三角恒等式改写

sin (x) + 3 cos (x) = 0

在两边除以

cos (x), cos (x) \neq = 0

\frac{sin ( x ) + 3 cos ( x )}{cos ( x )} = \frac{0}{cos ( x )}

化简

\frac{sin ( x )}{cos ( x )} + 3 = 0

使用基本三角恒等式:

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

tan (x) + 3 = 0

tan (x) + 3 = 0

将

3

到右边

tan (x) + 3 = 0

两边减去

3

tan (x) + 3 - 3 = 0 - 3

化简

tan (x) = - 3

tan (x) = - 3

使用反三角函数性质

tan (x) = - 3

tan (x) = - 3

的通解

tan (x) = - a \Rightarrow x = arctan (- a) + πn

x = arctan (- 3) + πn

x = arctan (- 3) + πn

合并所有解

x = \frac{π}{4} + πn, x = arctan (- 3) + πn

合并所有解

x = 2 πn, x = π + 2 πn, x = \frac{π}{4} + πn, x = arctan (- 3) + πn

以小数形式表示解

x = 2 πn, x = π + 2 πn, x = \frac{π}{4} + πn, x = - 1.24904 \dots + πn

作图

流行的例子

cot (x) = \frac{15}{8}

cos (θ) = \frac{- 5}{4}

solvefor x,y=5cos(8x)-y

so l v e f or x, y = 5 cos (8 x) - y

csc(θ)= 3/2 , pi/2 <θ<(3pi)/2

csc (θ) = \frac{3}{2}, \frac{π}{2} < θ < \frac{3 π}{2}

tan(x)=(5.1)/(4.2)

tan (x) = \frac{5.1}{4.2}