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受欢迎的三角函数 >

sin(x)+sqrt(3)cos(x)=2

解答

sin (x) + 3 cos (x) = 2

解答

x = \frac{π}{6} + 2 πn

+1

度数

x = 3 0^{\circ} + 36 0^{\circ} n

求解步骤

sin (x) + 3 cos (x) = 2

两边减去

3 cos (x)

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

两边进行平方

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

两边减去

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

sin^{2} (x) - 4 + 43 cos (x) - 3 cos^{2} (x) = 0

使用三角恒等式改写

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

使用毕达哥拉斯恒等式:

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

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

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

化简

- 4 + 1 - cos^{2} (x) - 3 cos^{2} (x) + 4 cos (x) 3 : 43 cos (x) - 4 cos^{2} (x) - 3

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

同类项相加:

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

= - 4 + 1 - 4 cos^{2} (x) + 43 cos (x)

数字相加/相减:

- 4 + 1 = - 3

= 43 cos (x) - 4 cos^{2} (x) - 3

= 43 cos (x) - 4 cos^{2} (x) - 3

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

用替代法求解

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

令

: cos (x) = u

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

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

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

改写成标准形式

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

- 4 u^{2} + 43 u - 3 = 0

使用求根公式求解

- 4 u^{2} + 43 u - 3 = 0

二次方程求根公式:

若

a = - 4, b = 43, c = - 3

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

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

(43)^{2} - 4 (- 4) (- 3) = 0

(43)^{2} - 4 (- 4) (- 3)

使用法则

- (- a) = a

= (43)^{2} - 4 \cdot 4 \cdot 3

(43)^{2} = 4^{2} \cdot 3

(43)^{2}

使用指数法则:

(a \cdot b)^{n} = a^{n} b^{n}

= 4^{2} (3)^{2}

(3)^{2} : 3

使用根式运算法则:

a = a^{\frac{1}{2}}

= (3^{\frac{1}{2}})^{2}

使用指数法则:

(a^{b})^{c} = a^{b c}

= 3^{\frac{1}{2} \cdot 2}

\frac{1}{2} \cdot 2 = 1

\frac{1}{2} \cdot 2

分式相乘:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{1 \cdot 2}{2}

约分:

2

= 1

= 3

= 4^{2} \cdot 3

4 \cdot 4 \cdot 3 = 48

4 \cdot 4 \cdot 3

数字相乘:

4 \cdot 4 \cdot 3 = 48

= 48

= 4^{2} \cdot 3 - 48

4^{2} \cdot 3 = 48

4^{2} \cdot 3

4^{2} = 16

= 16 \cdot 3

数字相乘:

16 \cdot 3 = 48

= 48

= 48 - 48

数字相减:

48 - 48 = 0

= 0

u_{1, 2} = \frac{- 4 3 \pm 0}{2 ( - 4 )}

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

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

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

去除括号:

(- a) = - a

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

数字相乘:

2 \cdot 4 = 8

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

使用分式法则:

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

= \frac{4 3}{8}

约分:

4

= \frac{3}{2}

u = \frac{3}{2}

二次方程组的解是:

u = \frac{3}{2}

u = cos (x)

代回

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

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

cos (x) = \frac{3}{2} : x = \frac{π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

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

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

的通解

cos (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} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{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} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

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

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

合并所有解

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

将解代入原方程进行验证

将它们代入

sin (x) + 3 cos (x) = 2

检验解是否符合

去除与方程不符的解。

检验

\frac{π}{6} + 2 πn

的解:

真

\frac{π}{6} + 2 πn

代入

n = 1

\frac{π}{6} + 2 π 1

对于

sin (x) + 3 cos (x) = 2

代入

x = \frac{π}{6} + 2 π 1

sin (\frac{π}{6} + 2 π 1) + 3 cos (\frac{π}{6} + 2 π 1) = 2

整理后得

2 = 2

\Rightarrow 真

检验

\frac{11 π}{6} + 2 πn

的解:

假

\frac{11 π}{6} + 2 πn

代入

n = 1

\frac{11 π}{6} + 2 π 1

对于

sin (x) + 3 cos (x) = 2

代入

x = \frac{11 π}{6} + 2 π 1

sin (\frac{11 π}{6} + 2 π 1) + 3 cos (\frac{11 π}{6} + 2 π 1) = 2

整理后得

1 = 2

\Rightarrow 假

x = \frac{π}{6} + 2 πn

作图

流行的例子

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3 tan^{4} (θ) - 10 tan^{2} (θ) + 3 = 0

cos (x) = 0.9

4sin^2(θ/2)+8cos(θ/2)-7=0

4 sin^{2} (\frac{θ}{2}) + 8 cos (\frac{θ}{2}) - 7 = 0

11sin(x)+5=sin(x)

11 sin (x) + 5 = sin (x)

cos (x) = 2 sin (x)