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受欢迎的三角函数 >

14sin^2(x)+21sin(x)+7=0

解答

14 sin^{2} (x) + 21 sin (x) + 7 = 0

解答

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn, x = \frac{3 π}{2} + 2 πn

+1

度数

x = 21 0^{\circ} + 36 0^{\circ} n, x = 33 0^{\circ} + 36 0^{\circ} n, x = 27 0^{\circ} + 36 0^{\circ} n

求解步骤

14 sin^{2} (x) + 21 sin (x) + 7 = 0

用替代法求解

14 sin^{2} (x) + 21 sin (x) + 7 = 0

令

: sin (x) = u

14 u^{2} + 21 u + 7 = 0

14 u^{2} + 21 u + 7 = 0 : u = - \frac{1}{2}, u = - 1

14 u^{2} + 21 u + 7 = 0

使用求根公式求解

14 u^{2} + 21 u + 7 = 0

二次方程求根公式:

若

a = 14, b = 21, c = 7

u_{1, 2} = \frac{- 21 \pm 2 1 ^{2} - 4 \cdot 14 \cdot 7}{2 \cdot 14}

u_{1, 2} = \frac{- 21 \pm 2 1 ^{2} - 4 \cdot 14 \cdot 7}{2 \cdot 14}

2 1^{2} - 4 \cdot 14 \cdot 7 = 7

2 1^{2} - 4 \cdot 14 \cdot 7

数字相乘:

4 \cdot 14 \cdot 7 = 392

= 2 1^{2} - 392

2 1^{2} = 441

= 441 - 392

数字相减:

441 - 392 = 49

= 49

因式分解数字:

49 = 7^{2}

= 7^{2}

使用根式运算法则:

n a^{n} = a

7^{2} = 7

= 7

u_{1, 2} = \frac{- 21 \pm 7}{2 \cdot 14}

将解分隔开

u_{1} = \frac{- 21 + 7}{2 \cdot 14}, u_{2} = \frac{- 21 - 7}{2 \cdot 14}

u = \frac{- 21 + 7}{2 \cdot 14} : - \frac{1}{2}

\frac{- 21 + 7}{2 \cdot 14}

数字相加/相减:

- 21 + 7 = - 14

= \frac{- 14}{2 \cdot 14}

数字相乘:

2 \cdot 14 = 28

= \frac{- 14}{28}

使用分式法则:

\frac{- a}{b} = - \frac{a}{b}

= - \frac{14}{28}

约分:

14

= - \frac{1}{2}

u = \frac{- 21 - 7}{2 \cdot 14} : - 1

\frac{- 21 - 7}{2 \cdot 14}

数字相减:

- 21 - 7 = - 28

= \frac{- 28}{2 \cdot 14}

数字相乘:

2 \cdot 14 = 28

= \frac{- 28}{28}

使用分式法则:

\frac{- a}{b} = - \frac{a}{b}

= - \frac{28}{28}

使用法则

\frac{a}{a} = 1

= - 1

二次方程组的解是:

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

u = sin (x)

代回

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

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

sin (x) = - \frac{1}{2} : x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

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

sin (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}

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

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

合并所有解

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn, x = \frac{3 π}{2} + 2 πn

作图

流行的例子

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