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受欢迎的三角函数 >

sec^2(x)<= tan^2(x)+sec(x)

解答

sec^{2} (x) \leq tan^{2} (x) + sec (x)

解答

2 πn \leq x < \frac{π}{2} + 2 πn or \frac{3 π}{2} + 2 πn < x \leq 2 π + 2 πn

+2

间隔符号

[2 πn, \frac{π}{2} + 2 πn) \cup (\frac{3 π}{2} + 2 πn, 2 π + 2 πn]

十进制

2 πn \leq x < 1.57079 \dots + 2 πn or 4.71238 \dots + 2 πn < x \leq 6.28318 \dots + 2 πn

求解步骤

sec^{2} (x) \leq tan^{2} (x) + sec (x)

两边减去

tan^{2} (x) + sec (x)

sec^{2} (x) - (tan^{2} (x) + sec (x)) \leq tan^{2} (x) + sec (x) - (tan^{2} (x) + sec (x))

sec^{2} (x) - (tan^{2} (x) + sec (x)) \leq 0

sec^{2} (x) - (tan^{2} (x) + sec (x))

的周期:

2 π

周期函数和的复合周期是这些周期的最小公倍数

sec^{2} (x), (tan^{2} (x) + sec (x))

sec^{2} (x)

的周期:

π

sec^{n} (x)

的周期

= \frac{sec ( x ) 的周期}{2}

，前提是 n 为偶数

sec (x)

的周期:

2 π

sec (x)

的周期是

2 π

= 2 π

\frac{2 π}{2}

化简

π

(tan^{2} (x) + sec (x))

的周期:

2 π

(tan^{2} (x) + sec (x))

包含以下函数及对应周期:

sec (x)

的周期为

2 π

复合周期为:

2 π

合并周期:

π, 2 π

= 2 π

用 sin, cos 表示

sec^{2} (x) - (tan^{2} (x) + sec (x)) \leq 0

使用基本三角恒等式:

sec (x) = \frac{1}{cos ( x )}

(\frac{1}{cos ( x )})^{2} - (tan^{2} (x) + \frac{1}{cos ( x )}) \leq 0

使用基本三角恒等式:

tan (x) = \frac{sin ( x )}{cos ( x )}

(\frac{1}{cos ( x )})^{2} - ((\frac{sin ( x )}{cos ( x )})^{2} + \frac{1}{cos ( x )}) \leq 0

(\frac{1}{cos ( x )})^{2} - ((\frac{sin ( x )}{cos ( x )})^{2} + \frac{1}{cos ( x )}) \leq 0

化简

(\frac{1}{cos ( x )})^{2} - ((\frac{sin ( x )}{cos ( x )})^{2} + \frac{1}{cos ( x )}) : \frac{1 - sin ^{2} ( x ) - cos ( x )}{cos ^{2} ( x )}

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

(\frac{1}{cos ( x )})^{2} = \frac{1}{cos ^{2} ( x )}

(\frac{1}{cos ( x )})^{2}

使用指数法则:

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

= \frac{1 ^{2}}{cos ^{2} ( x )}

使用法则

1^{a} = 1

1^{2} = 1

= \frac{1}{cos ^{2} ( x )}

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

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

使用指数法则:

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

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

化简

\frac{sin ^{2} ( x )}{cos ^{2} ( x )} + \frac{1}{cos ( x )} : \frac{sin ^{2} ( x ) + cos ( x )}{cos ^{2} ( x )}

\frac{sin ^{2} ( x )}{cos ^{2} ( x )} + \frac{1}{cos ( x )}

cos^{2} (x), cos (x)

的最小公倍数:

cos^{2} (x)

cos^{2} (x), cos (x)

最小公倍数 (LCM)

计算出由出现在

cos^{2} (x)

或

cos (x)

中的因子组成的表达式

= cos^{2} (x)

根据最小公倍数调整分式

将每个分子乘以其分母转变为最小公倍数所要乘以的同一数值

cos^{2} (x)

对于

\frac{1}{cos ( x )} :

将分母和分子乘以

cos (x)

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

= \frac{sin ^{2} ( x )}{cos ^{2} ( x )} + \frac{cos ( x )}{cos ^{2} ( x )}

因为分母相等，所以合并分式:

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

= \frac{sin ^{2} ( x ) + cos ( x )}{cos ^{2} ( x )}

= - \frac{sin ^{2} ( x ) + cos ( x )}{cos ^{2} ( x )}

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

使用法则

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

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

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

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

打开括号

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

使用加减运算法则

+ (- a) = - a

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

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

\frac{1 - sin ^{2} ( x ) - cos ( x )}{cos ^{2} ( x )} \leq 0

确定

0 \leq x < 2 π

时

\frac{1 - sin ^{2} ( x ) - cos ( x )}{cos ^{2} ( x )}

的零点和无定义点

要找到零点，将不等式设置为零

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

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

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

\frac{f ( x )}{g ( x )} = 0 \Rightarrow f (x) = 0

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

使用三角恒等式改写

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

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

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

用替代法求解

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

令

: cos (x) = u

- u + u^{2} = 0

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

- u + u^{2} = 0

改写成标准形式

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

u^{2} - u = 0

使用求根公式求解

u^{2} - u = 0

二次方程求根公式:

若

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

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

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

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

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

(- 1)^{2} = 1

(- 1)^{2}

使用指数法则:

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

若

n

是偶数

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

= 1^{2}

使用法则

1^{a} = 1

= 1

4 \cdot 1 \cdot 0 = 0

4 \cdot 1 \cdot 0

使用法则

0 \cdot a = 0

= 0

= 1 - 0

数字相减:

1 - 0 = 1

= 1

使用法则

1 = 1

= 1

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

将解分隔开

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

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

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

使用法则

- (- a) = a

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

数字相加:

1 + 1 = 2

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

数字相乘:

2 \cdot 1 = 2

= \frac{2}{2}

使用法则

\frac{a}{a} = 1

= 1

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

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

使用法则

- (- a) = a

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

数字相减:

1 - 1 = 0

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

数字相乘:

2 \cdot 1 = 2

= \frac{0}{2}

使用法则

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

= 0

二次方程组的解是:

u = 1, u = 0

u = cos (x)

代回

cos (x) = 1, cos (x) = 0

cos (x) = 1, cos (x) = 0

cos (x) = 1, 0 \leq x < 2 π : x = 0

cos (x) = 1, 0 \leq x < 2 π

cos (x) = 1

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 = 0 + 2 πn

x = 0 + 2 πn

解

x = 0 + 2 πn : x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn

在

0 \leq x < 2 π

范围内的解

x = 0

cos (x) = 0, 0 \leq x < 2 π : x = \frac{π}{2}, x = \frac{3 π}{2}

cos (x) = 0, 0 \leq x < 2 π

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

在

0 \leq x < 2 π

范围内的解

x = \frac{π}{2}, x = \frac{3 π}{2}

合并所有解

x = 0, x = \frac{π}{2}, x = \frac{3 π}{2}

因为方程对以下值无定义:

\frac{π}{2}, \frac{3 π}{2}

x = 0

确定无定义点:

x = \frac{π}{2}, x = \frac{3 π}{2}

找到分母的零解

cos^{2} (x) = 0

使用法则

x^{n} = 0 \Rightarrow x = 0

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

在

0 \leq x < 2 π

范围内的解

x = \frac{π}{2}, x = \frac{3 π}{2}

0, \frac{π}{2}, \frac{3 π}{2}

确定区间

0 < x < \frac{π}{2}, \frac{π}{2} < x < \frac{3 π}{2}, \frac{3 π}{2} < x < 2 π

总结如下表：

1 - sin^{2} (x) - cos (x) cos^{2} (x) \frac{1 - s i n ^{2} ( x ) - c o s ( x )}{c o s ^{2} ( x )} x = 0 0 + 0 0 < x < \frac{π}{2} - + - x = \frac{π}{2} 00 未定义 \frac{π}{2} < x < \frac{3 π}{2} + + + x = \frac{3 π}{2} 00 未定义 \frac{3 π}{2} < x < 2 π - + - x = 2 π 0 + 0

确定满足所需条件的区间：

\leq 0

x = 0 or 0 < x < \frac{π}{2} or \frac{3 π}{2} < x < 2 π or x = 2 π

合并重叠的区间

0 \leq x < \frac{π}{2} or \frac{3 π}{2} < x < 2 π or x = 2 π

两个区间的并集是指存在于任一区间的数的集合

x = 0

or

0 < x < \frac{π}{2}

0 \leq x < \frac{π}{2}

两个区间的并集是指存在于任一区间的数的集合

0 \leq x < \frac{π}{2}

or

\frac{3 π}{2} < x < 2 π

0 \leq x < \frac{π}{2} or \frac{3 π}{2} < x < 2 π

两个区间的并集是指存在于任一区间的数的集合

0 \leq x < \frac{π}{2} or \frac{3 π}{2} < x < 2 π

or

x = 2 π

0 \leq x < \frac{π}{2} or \frac{3 π}{2} < x \leq 2 π

0 \leq x < \frac{π}{2} or \frac{3 π}{2} < x \leq 2 π

使用周期

sec^{2} (x) - (tan^{2} (x) + sec (x))

2 πn \leq x < \frac{π}{2} + 2 πn or \frac{3 π}{2} + 2 πn < x \leq 2 π + 2 πn

流行的例子

sin(x)-sqrt(3)cos(x)<= 0

sin (x) - 3 cos (x) \leq 0

(4cos^2(x)-3)/(sin(x)+cos(x)+5)<0

\frac{4 cos ^{2} ( x ) - 3}{sin ( x ) + cos ( x ) + 5} < 0

cos (t) \geq 0

- 1 + tan (x) \leq 1

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

cos (x) (2 sin (x) - 1) \leq 0, - π < x \leq π