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受欢迎的三角函数 >

csc^2(x)-2csc(x)=2-4sin(x)

解答

csc^{2} (x) - 2 csc (x) = 2 - 4 sin (x)

解答

x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn, x = \frac{5 π}{4} + 2 πn, x = \frac{7 π}{4} + 2 πn, x = \frac{π}{4} + 2 πn, x = \frac{3 π}{4} + 2 πn

+1

度数

x = 3 0^{\circ} + 36 0^{\circ} n, x = 15 0^{\circ} + 36 0^{\circ} n, x = 22 5^{\circ} + 36 0^{\circ} n, x = 31 5^{\circ} + 36 0^{\circ} n, x = 4 5^{\circ} + 36 0^{\circ} n, x = 13 5^{\circ} + 36 0^{\circ} n

求解步骤

csc^{2} (x) - 2 csc (x) = 2 - 4 sin (x)

两边减去

2 - 4 sin (x)

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

使用三角恒等式改写

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

使用基本三角恒等式:

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

= - 2 + csc^{2} (x) - 2 csc (x) + 4 \cdot \frac{1}{csc ( x )}

4 \cdot \frac{1}{csc ( x )} = \frac{4}{csc ( x )}

4 \cdot \frac{1}{csc ( x )}

分式相乘:

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

= \frac{1 \cdot 4}{csc ( x )}

数字相乘:

1 \cdot 4 = 4

= \frac{4}{csc ( x )}

= - 2 + csc^{2} (x) - 2 csc (x) + \frac{4}{csc ( x )}

- 2 + csc^{2} (x) + \frac{4}{csc ( x )} - 2 csc (x) = 0

用替代法求解

- 2 + csc^{2} (x) + \frac{4}{csc ( x )} - 2 csc (x) = 0

令

: csc (x) = u

- 2 + u^{2} + \frac{4}{u} - 2 u = 0

- 2 + u^{2} + \frac{4}{u} - 2 u = 0 : u = 2, u = - 2, u = 2

- 2 + u^{2} + \frac{4}{u} - 2 u = 0

在两边乘以

u

- 2 + u^{2} + \frac{4}{u} - 2 u = 0

在两边乘以

u

- 2 u + u^{2} u + \frac{4}{u} u - 2 uu = 0 \cdot u

化简

- 2 u + u^{2} u + \frac{4}{u} u - 2 uu = 0 \cdot u

化简

u^{2} u : u^{3}

u^{2} u

使用指数法则:

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

u^{2} u = u^{2 + 1}

= u^{2 + 1}

数字相加:

2 + 1 = 3

= u^{3}

化简

\frac{4}{u} u : 4

\frac{4}{u} u

分式相乘:

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

= \frac{4 u}{u}

约分:

u

= 4

化简

- 2 uu : - 2 u^{2}

- 2 uu

使用指数法则:

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

uu = u^{1 + 1}

= - 2 u^{1 + 1}

数字相加:

1 + 1 = 2

= - 2 u^{2}

化简

0 \cdot u : 0

0 \cdot u

使用法则

0 \cdot a = 0

= 0

- 2 u + u^{3} + 4 - 2 u^{2} = 0

- 2 u + u^{3} + 4 - 2 u^{2} = 0

- 2 u + u^{3} + 4 - 2 u^{2} = 0

解

- 2 u + u^{3} + 4 - 2 u^{2} = 0 : u = 2, u = - 2, u = 2

- 2 u + u^{3} + 4 - 2 u^{2} = 0

改写成标准形式

a_{n} x^{n} + \dots + a_{1} x + a_{0} = 0

u^{3} - 2 u^{2} - 2 u + 4 = 0

因式分解

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

u^{3} - 2 u^{2} - 2 u + 4

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

从

- 2 u + 4

分解出因式

- 2

:

- 2 (u - 2)

- 2 u + 4

将

4

改写为

2 \cdot 2

= - 2 u + 2 \cdot 2

因式分解出通项

- 2

= - 2 (u - 2)

从

u^{3} - 2 u^{2}

分解出因式

u^{2}

:

u^{2} (u - 2)

u^{3} - 2 u^{2}

使用指数法则:

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

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

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

因式分解出通项

u^{2}

= u^{2} (u - 2)

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

因式分解出通项

u - 2

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

分解

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

u^{2} - 2

使用根式运算法则:

a = (a)^{2}

2 = (2)^{2}

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

使用平方差公式:

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

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

= (u + 2) (u - 2)

= (u - 2) (u + 2) (u - 2)

(u - 2) (u + 2) (u - 2) = 0

使用零因数法则： If

ab = 0

then

a = 0

or

b = 0

u - 2 = 0 or u + 2 = 0 or u - 2 = 0

解

u - 2 = 0 : u = 2

u - 2 = 0

将

2

到右边

u - 2 = 0

两边加上

2

u - 2 + 2 = 0 + 2

化简

u = 2

u = 2

解

u + 2 = 0 : u = - 2

u + 2 = 0

将

2

到右边

u + 2 = 0

两边减去

2

u + 2 - 2 = 0 - 2

化简

u = - 2

u = - 2

解

u - 2 = 0 : u = 2

u - 2 = 0

将

2

到右边

u - 2 = 0

两边加上

2

u - 2 + 2 = 0 + 2

化简

u = 2

u = 2

解为

u = 2, u = - 2, u = 2

u = 2, u = - 2, u = 2

验证解

找到无定义的点（奇点）:

u = 0

取

- 2 + u^{2} + \frac{4}{u} - 2 u

的分母，令其等于零

u = 0

以下点无定义

u = 0

将不在定义域的点与解相综合:

u = 2, u = - 2, u = 2

u = csc (x)

代回

csc (x) = 2, csc (x) = - 2, csc (x) = 2

csc (x) = 2, csc (x) = - 2, csc (x) = 2

csc (x) = 2 : x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

csc (x) = 2

csc (x) = 2

的通解

csc (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} csc (x) Undefiend 22 \frac{2 3}{3} 1 \frac{2 3}{3} 22 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} csc (x) Undefiend - 2 - 2 - \frac{2 3}{3} - 1 - \frac{2 3}{3} - 2 - 2

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

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

csc (x) = - 2 : x = \frac{5 π}{4} + 2 πn, x = \frac{7 π}{4} + 2 πn

csc (x) = - 2

csc (x) = - 2

的通解

csc (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} csc (x) Undefiend 22 \frac{2 3}{3} 1 \frac{2 3}{3} 22 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} csc (x) Undefiend - 2 - 2 - \frac{2 3}{3} - 1 - \frac{2 3}{3} - 2 - 2

x = \frac{5 π}{4} + 2 πn, x = \frac{7 π}{4} + 2 πn

x = \frac{5 π}{4} + 2 πn, x = \frac{7 π}{4} + 2 πn

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

csc (x) = 2

csc (x) = 2

的通解

csc (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} csc (x) Undefiend 22 \frac{2 3}{3} 1 \frac{2 3}{3} 22 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} csc (x) Undefiend - 2 - 2 - \frac{2 3}{3} - 1 - \frac{2 3}{3} - 2 - 2

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

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

合并所有解

x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn, x = \frac{5 π}{4} + 2 πn, x = \frac{7 π}{4} + 2 πn, x = \frac{π}{4} + 2 πn, x = \frac{3 π}{4} + 2 πn

作图

流行的例子

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

cos(θ)=-1/(sqrt(2))

cos (θ) = - \frac{1}{2}

3 sin (2 t) + 4 = 1

solvefor x,cos(x)=0

so l v e f or x, cos (x) = 0

cos(x+pi/6)-cos(x-pi/6)=1

cos (x + \frac{π}{6}) - cos (x - \frac{π}{6}) = 1