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受欢迎的三角函数 >

sin(2x)=cos(40)

解答

sin (2 x) = cos (4 0^{\circ})

解答

x = \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}, x = \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

+1

弧度

x = \frac{5 π}{36} + \frac{36 π}{36} n, x = \frac{13 π}{36} + \frac{36 π}{36} n

求解步骤

sin (2 x) = cos (4 0^{\circ})

使用三角恒等式改写

cos (4 0^{\circ})

利用以下特性:

cos (x) = sin (9 0^{\circ} - x)

sin (9 0^{\circ} - 4 0^{\circ})

sin (2 x) = sin (9 0^{\circ} - 4 0^{\circ})

使用反三角函数性质

sin (2 x) = sin (9 0^{\circ} - 4 0^{\circ})

sin (x) = sin (y) \Rightarrow x = y + 2 π n, x = π - y + 2 π n

2 x = 9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n, 2 x = 18 0^{\circ} - (9 0^{\circ} - 4 0^{\circ}) + 36 0^{\circ} n

2 x = 9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n, 2 x = 18 0^{\circ} - (9 0^{\circ} - 4 0^{\circ}) + 36 0^{\circ} n

2 x = 9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n : x = \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}

2 x = 9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n

两边除以

2

2 x = 9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n

两边除以

2

\frac{2 x}{2} = \frac{9 0 ^{\circ}}{2} - \frac{4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2}

化简

\frac{2 x}{2} = \frac{9 0 ^{\circ}}{2} - \frac{4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2}

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

\frac{9 0 ^{\circ}}{2} - \frac{4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2} : \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}

\frac{9 0 ^{\circ}}{2} - \frac{4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2}

使用法则

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

= \frac{9 0 ^{\circ} - 4 0 ^{\circ} + 36 0 ^{\circ} n}{2}

化简

9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n : \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{18}

9 0^{\circ} - 4 0^{\circ} + 36 0^{\circ} n

将项转换为分式:

36 0^{\circ} n = \frac{36 0 ^{\circ} n}{1}

= 9 0^{\circ} - 4 0^{\circ} + \frac{36 0 ^{\circ} n}{1}

2, 9, 1

的最小公倍数:

18

2, 9, 1

最小公倍数 (LCM)

2

质因数分解:

2

2

2

是质数，因此无法因数分解

= 2

9

质因数分解:

3 \cdot 3

9

9

除以

39 = 3 \cdot 3

= 3 \cdot 3

1

质因数分解

计算出由至少在以下一个数字中出现的因数组成的数字:

2, 9, 1

= 2 \cdot 3 \cdot 3

数字相乘:

2 \cdot 3 \cdot 3 = 18

= 18

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

18

对于

9 0^{\circ} :

将分母和分子乘以

9

9 0^{\circ} = \frac{18 0 ^{\circ} 9}{2 \cdot 9} = 9 0^{\circ}

对于

4 0^{\circ} :

将分母和分子乘以

2

4 0^{\circ} = \frac{36 0 ^{\circ} 2}{9 \cdot 2} = 4 0^{\circ}

对于

\frac{36 0 ^{\circ} n}{1} :

将分母和分子乘以

18

\frac{36 0 ^{\circ} n}{1} = \frac{36 0 ^{\circ} n \cdot 18}{1 \cdot 18} = \frac{648 0 ^{\circ} n}{18}

= 9 0^{\circ} - 4 0^{\circ} + \frac{648 0 ^{\circ} n}{18}

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{18 0 ^{\circ} 9 - 72 0 ^{\circ} + 648 0 ^{\circ} n}{18}

同类项相加:

162 0^{\circ} - 72 0^{\circ} = 90 0^{\circ}

= \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{18}

= \frac{\frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{18}}{2}

使用分式法则:

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

= \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{18 \cdot 2}

数字相乘:

18 \cdot 2 = 36

= \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}

2 x = 18 0^{\circ} - (9 0^{\circ} - 4 0^{\circ}) + 36 0^{\circ} n : x = \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

2 x = 18 0^{\circ} - (9 0^{\circ} - 4 0^{\circ}) + 36 0^{\circ} n

两边除以

2

2 x = 18 0^{\circ} - (9 0^{\circ} - 4 0^{\circ}) + 36 0^{\circ} n

两边除以

2

\frac{2 x}{2} = 9 0^{\circ} - \frac{9 0 ^{\circ} - 4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2}

化简

\frac{2 x}{2} = 9 0^{\circ} - \frac{9 0 ^{\circ} - 4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2}

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

9 0^{\circ} - \frac{9 0 ^{\circ} - 4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2} : \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

9 0^{\circ} - \frac{9 0 ^{\circ} - 4 0 ^{\circ}}{2} + \frac{36 0 ^{\circ} n}{2}

使用法则

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

= \frac{18 0 ^{\circ} - ( 9 0 ^{\circ} - 4 0 ^{\circ} ) + 36 0 ^{\circ} n}{2}

化简

9 0^{\circ} - 4 0^{\circ} : 5 0^{\circ}

9 0^{\circ} - 4 0^{\circ}

2, 9

的最小公倍数:

18

2, 9

最小公倍数 (LCM)

2

质因数分解:

2

2

2

是质数，因此无法因数分解

= 2

9

质因数分解:

3 \cdot 3

9

9

除以

39 = 3 \cdot 3

= 3 \cdot 3

将每个因子乘以它在

2

或

9

中出现的最多次数

= 2 \cdot 3 \cdot 3

数字相乘:

2 \cdot 3 \cdot 3 = 18

= 18

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

18

对于

9 0^{\circ} :

将分母和分子乘以

9

9 0^{\circ} = \frac{18 0 ^{\circ} 9}{2 \cdot 9} = 9 0^{\circ}

对于

4 0^{\circ} :

将分母和分子乘以

2

4 0^{\circ} = \frac{36 0 ^{\circ} 2}{9 \cdot 2} = 4 0^{\circ}

= 9 0^{\circ} - 4 0^{\circ}

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{18 0 ^{\circ} 9 - 72 0 ^{\circ}}{18}

同类项相加:

162 0^{\circ} - 72 0^{\circ} = 90 0^{\circ}

= 5 0^{\circ}

= \frac{18 0 ^{\circ} - 5 0 ^{\circ} + 36 0 ^{\circ} n}{2}

化简

18 0^{\circ} - 5 0^{\circ} + 36 0^{\circ} n : \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{18}

18 0^{\circ} - 5 0^{\circ} + 36 0^{\circ} n

将项转换为分式:

18 0^{\circ} = 18 0^{\circ}, 36 0^{\circ} n = \frac{36 0 ^{\circ} n 18}{18}

= 18 0^{\circ} - 5 0^{\circ} + \frac{36 0 ^{\circ} n \cdot 18}{18}

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{18 0 ^{\circ} 18 - 90 0 ^{\circ} + 36 0 ^{\circ} n \cdot 18}{18}

18 0^{\circ} 18 - 90 0^{\circ} + 36 0^{\circ} n \cdot 18 = 234 0^{\circ} + 648 0^{\circ} n

18 0^{\circ} 18 - 90 0^{\circ} + 36 0^{\circ} n \cdot 18

同类项相加:

324 0^{\circ} - 90 0^{\circ} = 234 0^{\circ}

= 234 0^{\circ} + 2 \cdot 324 0^{\circ} n

数字相乘:

2 \cdot 18 = 36

= 234 0^{\circ} + 648 0^{\circ} n

= \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{18}

= \frac{\frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{18}}{2}

使用分式法则:

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

= \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{18 \cdot 2}

数字相乘:

18 \cdot 2 = 36

= \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

x = \frac{90 0 ^{\circ} + 648 0 ^{\circ} n}{36}, x = \frac{234 0 ^{\circ} + 648 0 ^{\circ} n}{36}

作图

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