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受欢迎的三角函数 >

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

解答

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

解答

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

+1

度数

x = 9 0^{\circ} + 36 0^{\circ} n, x = 27 0^{\circ} + 36 0^{\circ} n

求解步骤

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

使用三角恒等式改写

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

使用毕达哥拉斯恒等式:

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

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

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

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

用替代法求解

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

令

: cos (x) = u

- u^{2} + 3 u = 0

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

- u^{2} + 3 u = 0

使用求根公式求解

- u^{2} + 3 u = 0

二次方程求根公式:

若

a = - 1, b = 3, c = 0

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

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

3^{2} - 4 (- 1) \cdot 0 = 3

3^{2} - 4 (- 1) \cdot 0

使用法则

- (- a) = a

= 3^{2} + 4 \cdot 1 \cdot 0

使用法则

0 \cdot a = 0

= 3^{2} + 0

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

= 3^{2}

使用根式运算法则:

n a^{n} = a,

假定

a \geq 0

= 3

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

将解分隔开

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

u = \frac{- 3 + 3}{2 ( - 1 )} : 0

\frac{- 3 + 3}{2 ( - 1 )}

去除括号:

(- a) = - a

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

数字相加/相减:

- 3 + 3 = 0

= \frac{0}{- 2 \cdot 1}

数字相乘:

2 \cdot 1 = 2

= \frac{0}{- 2}

使用分式法则:

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

= - \frac{0}{2}

使用法则

\frac{0}{a} = 0, a \neq = 0

= - 0

= 0

u = \frac{- 3 - 3}{2 ( - 1 )} : 3

\frac{- 3 - 3}{2 ( - 1 )}

去除括号:

(- a) = - a

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

数字相减:

- 3 - 3 = - 6

= \frac{- 6}{- 2 \cdot 1}

数字相乘:

2 \cdot 1 = 2

= \frac{- 6}{- 2}

使用分式法则:

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

= \frac{6}{2}

数字相除:

\frac{6}{2} = 3

= 3

二次方程组的解是:

u = 0, u = 3

u = cos (x)

代回

cos (x) = 0, cos (x) = 3

cos (x) = 0, cos (x) = 3

cos (x) = 0 : x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn

cos (x) = 0

cos (x) = 0

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}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn

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

cos (x) = 3 :

无解

cos (x) = 3

- 1 \leq cos (x) \leq 1

无解

合并所有解

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

作图

流行的例子

cos((3x-7)/2)=0

cos (\frac{3 x - 7}{2}) = 0

3tan^2(x)= 8/(sin^2(x))

3 tan^{2} (x) = \frac{8}{sin ^{2} ( x )}

sin^2(x)+sin^{22}(x)+sin^{23}(x)=1

sin^{2} (x) + sin^{22} (x) + sin^{23} (x) = 1

5sin(1.75x)=1.4

5 sin (1.75 x) = 1.4

cos (a - 5) = 0.675