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受欢迎的三角函数 >

2tan^2(x)+9tan(x)+7=0

解答

2 tan^{2} (x) + 9 tan (x) + 7 = 0

解答

x = \frac{3 π}{4} + πn, x = - 1.29249 \dots + πn

+1

度数

x = 13 5^{\circ} + 18 0^{\circ} n, x = - 74.05460 \dots^{\circ} + 18 0^{\circ} n

求解步骤

2 tan^{2} (x) + 9 tan (x) + 7 = 0

用替代法求解

2 tan^{2} (x) + 9 tan (x) + 7 = 0

令

: tan (x) = u

2 u^{2} + 9 u + 7 = 0

2 u^{2} + 9 u + 7 = 0 : u = - 1, u = - \frac{7}{2}

2 u^{2} + 9 u + 7 = 0

使用求根公式求解

2 u^{2} + 9 u + 7 = 0

二次方程求根公式:

若

a = 2, b = 9, c = 7

u_{1, 2} = \frac{- 9 \pm 9 ^{2} - 4 \cdot 2 \cdot 7}{2 \cdot 2}

u_{1, 2} = \frac{- 9 \pm 9 ^{2} - 4 \cdot 2 \cdot 7}{2 \cdot 2}

9^{2} - 4 \cdot 2 \cdot 7 = 5

9^{2} - 4 \cdot 2 \cdot 7

数字相乘:

4 \cdot 2 \cdot 7 = 56

= 9^{2} - 56

9^{2} = 81

= 81 - 56

数字相减:

81 - 56 = 25

= 25

因式分解数字:

25 = 5^{2}

= 5^{2}

使用根式运算法则:

n a^{n} = a

5^{2} = 5

= 5

u_{1, 2} = \frac{- 9 \pm 5}{2 \cdot 2}

将解分隔开

u_{1} = \frac{- 9 + 5}{2 \cdot 2}, u_{2} = \frac{- 9 - 5}{2 \cdot 2}

u = \frac{- 9 + 5}{2 \cdot 2} : - 1

\frac{- 9 + 5}{2 \cdot 2}

数字相加/相减:

- 9 + 5 = - 4

= \frac{- 4}{2 \cdot 2}

数字相乘:

2 \cdot 2 = 4

= \frac{- 4}{4}

使用分式法则:

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

= - \frac{4}{4}

使用法则

\frac{a}{a} = 1

= - 1

u = \frac{- 9 - 5}{2 \cdot 2} : - \frac{7}{2}

\frac{- 9 - 5}{2 \cdot 2}

数字相减:

- 9 - 5 = - 14

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

数字相乘:

2 \cdot 2 = 4

= \frac{- 14}{4}

使用分式法则:

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

= - \frac{14}{4}

约分:

2

= - \frac{7}{2}

二次方程组的解是:

u = - 1, u = - \frac{7}{2}

u = tan (x)

代回

tan (x) = - 1, tan (x) = - \frac{7}{2}

tan (x) = - 1, tan (x) = - \frac{7}{2}

tan (x) = - 1 : x = \frac{3 π}{4} + πn

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{3 π}{4} + πn

x = \frac{3 π}{4} + πn

tan (x) = - \frac{7}{2} : x = arctan (- \frac{7}{2}) + πn

tan (x) = - \frac{7}{2}

使用反三角函数性质

tan (x) = - \frac{7}{2}

tan (x) = - \frac{7}{2}

的通解

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

x = arctan (- \frac{7}{2}) + πn

x = arctan (- \frac{7}{2}) + πn

合并所有解

x = \frac{3 π}{4} + πn, x = arctan (- \frac{7}{2}) + πn

以小数形式表示解

x = \frac{3 π}{4} + πn, x = - 1.29249 \dots + πn

作图

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