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受欢迎的三角函数 >

3sin^2(x)-4cos(x)+1=0

解答

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

解答

x = 0.84106 \dots + 2 πn, x = 2 π - 0.84106 \dots + 2 πn

+1

度数

x = 48.18968 \dots^{\circ} + 36 0^{\circ} n, x = 311.81031 \dots^{\circ} + 36 0^{\circ} n

求解步骤

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

使用三角恒等式改写

1 + 3 sin^{2} (x) - 4 cos (x)

使用毕达哥拉斯恒等式:

cos^{2} (x) + sin^{2} (x) = 1

sin^{2} (x) = 1 - cos^{2} (x)

= 1 + 3 (1 - cos^{2} (x)) - 4 cos (x)

化简

1 + 3 (1 - cos^{2} (x)) - 4 cos (x) : - 3 cos^{2} (x) - 4 cos (x) + 4

1 + 3 (1 - cos^{2} (x)) - 4 cos (x)

乘开

3 (1 - cos^{2} (x)) : 3 - 3 cos^{2} (x)

3 (1 - cos^{2} (x))

使用分配律:

a (b - c) = ab - a c

a = 3, b = 1, c = cos^{2} (x)

= 3 \cdot 1 - 3 cos^{2} (x)

数字相乘:

3 \cdot 1 = 3

= 3 - 3 cos^{2} (x)

= 1 + 3 - 3 cos^{2} (x) - 4 cos (x)

数字相加:

1 + 3 = 4

= - 3 cos^{2} (x) - 4 cos (x) + 4

= - 3 cos^{2} (x) - 4 cos (x) + 4

4 - 3 cos^{2} (x) - 4 cos (x) = 0

用替代法求解

4 - 3 cos^{2} (x) - 4 cos (x) = 0

令

: cos (x) = u

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

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

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

改写成标准形式

a x^{2} + b x + c = 0

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

使用求根公式求解

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

二次方程求根公式:

若

a = - 3, b = - 4, c = 4

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

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

(- 4)^{2} - 4 (- 3) \cdot 4 = 8

(- 4)^{2} - 4 (- 3) \cdot 4

使用法则

- (- a) = a

= (- 4)^{2} + 4 \cdot 3 \cdot 4

使用指数法则:

(- a)^{n} = a^{n},

若

n

是偶数

(- 4)^{2} = 4^{2}

= 4^{2} + 4 \cdot 3 \cdot 4

数字相乘:

4 \cdot 3 \cdot 4 = 48

= 4^{2} + 48

4^{2} = 16

= 16 + 48

数字相加:

16 + 48 = 64

= 64

因式分解数字:

64 = 8^{2}

= 8^{2}

使用根式运算法则:

n a^{n} = a

8^{2} = 8

= 8

u_{1, 2} = \frac{- ( - 4 ) \pm 8}{2 ( - 3 )}

将解分隔开

u_{1} = \frac{- ( - 4 ) + 8}{2 ( - 3 )}, u_{2} = \frac{- ( - 4 ) - 8}{2 ( - 3 )}

u = \frac{- ( - 4 ) + 8}{2 ( - 3 )} : - 2

\frac{- ( - 4 ) + 8}{2 ( - 3 )}

去除括号:

(- a) = - a, - (- a) = a

= \frac{4 + 8}{- 2 \cdot 3}

数字相加:

4 + 8 = 12

= \frac{12}{- 2 \cdot 3}

数字相乘:

2 \cdot 3 = 6

= \frac{12}{- 6}

使用分式法则:

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

= - \frac{12}{6}

数字相除:

\frac{12}{6} = 2

= - 2

u = \frac{- ( - 4 ) - 8}{2 ( - 3 )} : \frac{2}{3}

\frac{- ( - 4 ) - 8}{2 ( - 3 )}

去除括号:

(- a) = - a, - (- a) = a

= \frac{4 - 8}{- 2 \cdot 3}

数字相减:

4 - 8 = - 4

= \frac{- 4}{- 2 \cdot 3}

数字相乘:

2 \cdot 3 = 6

= \frac{- 4}{- 6}

使用分式法则:

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

= \frac{4}{6}

约分:

2

= \frac{2}{3}

二次方程组的解是:

u = - 2, u = \frac{2}{3}

u = cos (x)

代回

cos (x) = - 2, cos (x) = \frac{2}{3}

cos (x) = - 2, cos (x) = \frac{2}{3}

cos (x) = - 2 :

无解

cos (x) = - 2

- 1 \leq cos (x) \leq 1

无解

cos (x) = \frac{2}{3} : x = arccos (\frac{2}{3}) + 2 πn, x = 2 π - arccos (\frac{2}{3}) + 2 πn

cos (x) = \frac{2}{3}

使用反三角函数性质

cos (x) = \frac{2}{3}

cos (x) = \frac{2}{3}

的通解

cos (x) = a \Rightarrow x = arccos (a) + 2 πn, x = 2 π - arccos (a) + 2 πn

x = arccos (\frac{2}{3}) + 2 πn, x = 2 π - arccos (\frac{2}{3}) + 2 πn

x = arccos (\frac{2}{3}) + 2 πn, x = 2 π - arccos (\frac{2}{3}) + 2 πn

合并所有解

x = arccos (\frac{2}{3}) + 2 πn, x = 2 π - arccos (\frac{2}{3}) + 2 πn

以小数形式表示解

x = 0.84106 \dots + 2 πn, x = 2 π - 0.84106 \dots + 2 πn

作图

流行的例子

sin(x)-cos(2x)-1=0

sin (x) - cos (2 x) - 1 = 0

sin^2(x)=sqrt(3)

sin^{2} (x) = 3

solvefor x,c^2=a^2+b^2-2ab*cos(x)

so l v e f or x, c^{2} = a^{2} + b^{2} - 2 ab \cdot cos (x)

sin(-pi/8 c)=-14/14

sin (- \frac{π}{8} c) = - \frac{14}{14}

(25)/(sin(x))=(18)/(sin(36))

\frac{25}{sin ( x )} = \frac{18}{sin ( 3 6 ^{\circ} )}