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受欢迎的三角函数 >

2sin^2(x)+sin^3(x)-1=0

解答

2 sin^{2} (x) + sin^{3} (x) - 1 = 0

解答

x = \frac{3 π}{2} + 2 πn, x = 0.66623 \dots + 2 πn, x = π - 0.66623 \dots + 2 πn

+1

度数

x = 27 0^{\circ} + 36 0^{\circ} n, x = 38.17270 \dots^{\circ} + 36 0^{\circ} n, x = 141.82729 \dots^{\circ} + 36 0^{\circ} n

求解步骤

2 sin^{2} (x) + sin^{3} (x) - 1 = 0

用替代法求解

2 sin^{2} (x) + sin^{3} (x) - 1 = 0

令

: sin (x) = u

2 u^{2} + u^{3} - 1 = 0

2 u^{2} + u^{3} - 1 = 0 : u = - 1, u = \frac{- 1 + 5}{2}, u = \frac{- 1 - 5}{2}

2 u^{2} + u^{3} - 1 = 0

改写成标准形式

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

u^{3} + 2 u^{2} - 1 = 0

因式分解

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

u^{3} + 2 u^{2} - 1

使用有理根定理

a_{0} = 1, a_{n} = 1

a_{0}

的除数

: 1, a_{n}

的除数

: 1

因此，检验以下有理数:

\pm \frac{1}{1}

- \frac{1}{1}

是表达式的根，所以因式分解

u + 1

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

\frac{u ^{3} + 2 u ^{2} - 1}{u + 1} = u^{2} + u - 1

\frac{u ^{3} + 2 u ^{2} - 1}{u + 1}

对

\frac{u ^{3} + 2 u ^{2} - 1}{u + 1}

做除法:

\frac{u ^{3} + 2 u ^{2} - 1}{u + 1} = u^{2} + \frac{u ^{2} - 1}{u + 1}

将分子

u^{3} + 2 u^{2} - 1

与除数

u + 1

的首项系数相除：

\frac{u ^{3}}{u} = u^{2}

商 = u^{2}

将

u + 1

乘以

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

将

u^{3} + 2 u^{2} - 1

减去

u^{3} + u^{2}

得到新的余数

余数 = u^{2} - 1

因此

\frac{u ^{3} + 2 u ^{2} - 1}{u + 1} = u^{2} + \frac{u ^{2} - 1}{u + 1}

= u^{2} + \frac{u ^{2} - 1}{u + 1}

对

\frac{u ^{2} - 1}{u + 1}

做除法:

\frac{u ^{2} - 1}{u + 1} = u + \frac{- u - 1}{u + 1}

将分子

u^{2} - 1

与除数

u + 1

的首项系数相除：

\frac{u ^{2}}{u} = u

商 = u

将

u + 1

乘以

u : u^{2} + u

将

u^{2} - 1

减去

u^{2} + u

得到新的余数

余数 = - u - 1

因此

\frac{u ^{2} - 1}{u + 1} = u + \frac{- u - 1}{u + 1}

= u^{2} + u + \frac{- u - 1}{u + 1}

对

\frac{- u - 1}{u + 1}

做除法:

\frac{- u - 1}{u + 1} = - 1

将分子

- u - 1

与除数

u + 1

的首项系数相除：

\frac{- u}{u} = - 1

商 = - 1

将

u + 1

乘以

- 1 : - u - 1

将

- u - 1

减去

- u - 1

得到新的余数

余数 = 0

因此

\frac{- u - 1}{u + 1} = - 1

= u^{2} + u - 1

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

(u + 1) (u^{2} + u - 1) = 0

使用零因数法则： If

ab = 0

then

a = 0

or

b = 0

u + 1 = 0 or u^{2} + 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^{2} + u - 1 = 0 : u = \frac{- 1 + 5}{2}, u = \frac{- 1 - 5}{2}

u^{2} + u - 1 = 0

使用求根公式求解

u^{2} + u - 1 = 0

二次方程求根公式:

若

a = 1, b = 1, c = - 1

u_{1, 2} = \frac{- 1 \pm 1 ^{2} - 4 \cdot 1 \cdot ( - 1 )}{2 \cdot 1}

u_{1, 2} = \frac{- 1 \pm 1 ^{2} - 4 \cdot 1 \cdot ( - 1 )}{2 \cdot 1}

1^{2} - 4 \cdot 1 \cdot (- 1) = 5

1^{2} - 4 \cdot 1 \cdot (- 1)

使用法则

1^{a} = 1

1^{2} = 1

= 1 - 4 \cdot 1 \cdot (- 1)

使用法则

- (- a) = a

= 1 + 4 \cdot 1 \cdot 1

数字相乘:

4 \cdot 1 \cdot 1 = 4

= 1 + 4

数字相加:

1 + 4 = 5

= 5

u_{1, 2} = \frac{- 1 \pm 5}{2 \cdot 1}

将解分隔开

u_{1} = \frac{- 1 + 5}{2 \cdot 1}, u_{2} = \frac{- 1 - 5}{2 \cdot 1}

u = \frac{- 1 + 5}{2 \cdot 1} : \frac{- 1 + 5}{2}

\frac{- 1 + 5}{2 \cdot 1}

数字相乘:

2 \cdot 1 = 2

= \frac{- 1 + 5}{2}

u = \frac{- 1 - 5}{2 \cdot 1} : \frac{- 1 - 5}{2}

\frac{- 1 - 5}{2 \cdot 1}

数字相乘:

2 \cdot 1 = 2

= \frac{- 1 - 5}{2}

二次方程组的解是:

u = \frac{- 1 + 5}{2}, u = \frac{- 1 - 5}{2}

解为

u = - 1, u = \frac{- 1 + 5}{2}, u = \frac{- 1 - 5}{2}

u = sin (x)

代回

sin (x) = - 1, sin (x) = \frac{- 1 + 5}{2}, sin (x) = \frac{- 1 - 5}{2}

sin (x) = - 1, sin (x) = \frac{- 1 + 5}{2}, sin (x) = \frac{- 1 - 5}{2}

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

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{3 π}{2} + 2 πn

x = \frac{3 π}{2} + 2 πn

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

sin (x) = \frac{- 1 + 5}{2}

使用反三角函数性质

sin (x) = \frac{- 1 + 5}{2}

sin (x) = \frac{- 1 + 5}{2}

的通解

sin (x) = a \Rightarrow x = arcsin (a) + 2 πn, x = π - arcsin (a) + 2 πn

x = arcsin (\frac{- 1 + 5}{2}) + 2 πn, x = π - arcsin (\frac{- 1 + 5}{2}) + 2 πn

x = arcsin (\frac{- 1 + 5}{2}) + 2 πn, x = π - arcsin (\frac{- 1 + 5}{2}) + 2 πn

sin (x) = \frac{- 1 - 5}{2} :

无解

sin (x) = \frac{- 1 - 5}{2}

- 1 \leq sin (x) \leq 1

无解

合并所有解

x = \frac{3 π}{2} + 2 πn, x = arcsin (\frac{- 1 + 5}{2}) + 2 πn, x = π - arcsin (\frac{- 1 + 5}{2}) + 2 πn

以小数形式表示解

x = \frac{3 π}{2} + 2 πn, x = 0.66623 \dots + 2 πn, x = π - 0.66623 \dots + 2 πn

作图

流行的例子

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