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受欢迎的三角函数 >

cos^2(x)=2+2sin(x),0<= x<= 2pi

解答

cos^{2} (x) = 2 + 2 sin (x), 0 \leq x \leq 2 π

解答

x = \frac{3 π}{2}

+1

度数

x = 27 0^{\circ}

求解步骤

cos^{2} (x) = 2 + 2 sin (x), 0 \leq x \leq 2 π

两边减去

2 + 2 sin (x)

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

使用三角恒等式改写

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

使用毕达哥拉斯恒等式:

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

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

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

化简

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

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

用替代法求解

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

令

: sin (x) = u

- 1 - u^{2} - 2 u = 0

- 1 - u^{2} - 2 u = 0 : u = - 1

- 1 - u^{2} - 2 u = 0

改写成标准形式

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

- u^{2} - 2 u - 1 = 0

使用求根公式求解

- u^{2} - 2 u - 1 = 0

二次方程求根公式:

若

a = - 1, b = - 2, c = - 1

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

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

(- 2)^{2} - 4 (- 1) (- 1) = 0

(- 2)^{2} - 4 (- 1) (- 1)

使用法则

- (- a) = a

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

使用指数法则:

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

若

n

是偶数

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

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

数字相乘:

4 \cdot 1 \cdot 1 = 4

= 2^{2} - 4

2^{2} = 4

= 4 - 4

数字相减:

4 - 4 = 0

= 0

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

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

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

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

去除括号:

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

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

数字相乘:

2 \cdot 1 = 2

= \frac{2}{- 2}

使用分式法则:

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

= - \frac{2}{2}

使用法则

\frac{a}{a} = 1

= - 1

u = - 1

二次方程组的解是:

u = - 1

u = sin (x)

代回

sin (x) = - 1

sin (x) = - 1

sin (x) = - 1, 0 \leq x \leq 2 π : x = \frac{3 π}{2}

sin (x) = - 1, 0 \leq x \leq 2 π

sin (x) = - 1

的通解

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

x = \frac{3 π}{2} + 2 πn

x = \frac{3 π}{2} + 2 πn

在

0 \leq x \leq 2 π

范围内的解

x = \frac{3 π}{2}

合并所有解

x = \frac{3 π}{2}

作图

流行的例子

1-sec^2(x)=tan^2(x)

csc^2(x)=(1/(cos(x)))^2

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

2-10sec(x)=4-9sec(x)