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受欢迎的三角函数 >

2tan^2(x)+3tan(x)+1=0

解答

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

解答

x = - 0.46364 \dots + πn, x = \frac{3 π}{4} + πn

+1

度数

x = - 26.56505 \dots^{\circ} + 18 0^{\circ} n, x = 13 5^{\circ} + 18 0^{\circ} n

求解步骤

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

用替代法求解

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

令

: tan (x) = u

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

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

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

使用求根公式求解

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

二次方程求根公式:

若

a = 2, b = 3, c = 1

u_{1, 2} = \frac{- 3 \pm 3 ^{2} - 4 \cdot 2 \cdot 1}{2 \cdot 2}

u_{1, 2} = \frac{- 3 \pm 3 ^{2} - 4 \cdot 2 \cdot 1}{2 \cdot 2}

3^{2} - 4 \cdot 2 \cdot 1 = 1

3^{2} - 4 \cdot 2 \cdot 1

数字相乘:

4 \cdot 2 \cdot 1 = 8

= 3^{2} - 8

3^{2} = 9

= 9 - 8

数字相减:

9 - 8 = 1

= 1

使用法则

1 = 1

= 1

u_{1, 2} = \frac{- 3 \pm 1}{2 \cdot 2}

将解分隔开

u_{1} = \frac{- 3 + 1}{2 \cdot 2}, u_{2} = \frac{- 3 - 1}{2 \cdot 2}

u = \frac{- 3 + 1}{2 \cdot 2} : - \frac{1}{2}

\frac{- 3 + 1}{2 \cdot 2}

数字相加/相减:

- 3 + 1 = - 2

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

数字相乘:

2 \cdot 2 = 4

= \frac{- 2}{4}

使用分式法则:

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

= - \frac{2}{4}

约分:

2

= - \frac{1}{2}

u = \frac{- 3 - 1}{2 \cdot 2} : - 1

\frac{- 3 - 1}{2 \cdot 2}

数字相减:

- 3 - 1 = - 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

二次方程组的解是:

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

u = tan (x)

代回

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

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

tan (x) = - \frac{1}{2} : x = arctan (- \frac{1}{2}) + πn

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

使用反三角函数性质

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

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

的通解

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

x = arctan (- \frac{1}{2}) + πn

x = arctan (- \frac{1}{2}) + πn

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

合并所有解

x = arctan (- \frac{1}{2}) + πn, x = \frac{3 π}{4} + πn

以小数形式表示解

x = - 0.46364 \dots + πn, x = \frac{3 π}{4} + πn

作图

流行的例子

-arctan(t)=(4-pi)/4

- arctan (t) = \frac{4 - π}{4}

cos^2(x+30)= 1/4

cos^{2} (x + 3 0^{\circ}) = \frac{1}{4}

cos (5 7^{\circ}) = sin (x)

3cos(x)=2-cos(x)

3 cos (x) = 2 - cos (x)

2cos^2(3x)-3cos(3x)=-1,0<= x<= 2pi

2 cos^{2} (3 x) - 3 cos (3 x) = - 1, 0 \leq x \leq 2 π