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受欢迎的三角函数 >

(sin(120))/(tan(45)+sin(210)cos(300))

解答

\frac{sin ( 12 0 ^{\circ} )}{tan ( 4 5 ^{\circ} ) + sin ( 21 0 ^{\circ} ) cos ( 30 0 ^{\circ} )}

解答

\frac{2 3}{3}

+1

十进制

1.15470 \dots

求解步骤

\frac{sin ( 12 0 ^{\circ} )}{tan ( 4 5 ^{\circ} ) + sin ( 21 0 ^{\circ} ) cos ( 30 0 ^{\circ} )}

改写为

= sin (21 0^{\circ}) cos (30 0^{\circ}) + tan (4 5^{\circ})

使用三角恒等式改写:

sin (21 0^{\circ}) cos (30 0^{\circ}) = \frac{sin ( 15 0 ^{\circ} ) - sin ( 9 0 ^{\circ} )}{2}

sin (21 0^{\circ}) cos (30 0^{\circ})

使用积化和差恒等式:

sin (s) cos (t) = \frac{1}{2} (sin (s + t) + sin (s - t))

= \frac{1}{2} (sin (21 0^{\circ} + 30 0^{\circ}) + sin (21 0^{\circ} - 30 0^{\circ}))

化简

= \frac{sin ( 51 0 ^{\circ} ) + sin ( - 9 0 ^{\circ} )}{2}

利用以下特性:

sin (- x) = - sin (x)

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

= \frac{sin ( 51 0 ^{\circ} ) - sin ( 9 0 ^{\circ} )}{2}

sin (51 0^{\circ}) = sin (15 0^{\circ})

sin (51 0^{\circ})

将

51 0^{\circ}

改写为

36 0^{\circ} + 15 0^{\circ}

= sin (36 0^{\circ} + 15 0^{\circ})

使用周期

sin

:

sin (x + 36 0^{\circ}) = sin (x)

sin (36 0^{\circ} + 15 0^{\circ}) = sin (15 0^{\circ})

= sin (15 0^{\circ})

= \frac{sin ( 15 0 ^{\circ} ) - sin ( 9 0 ^{\circ} )}{2}

= \frac{sin ( 12 0 ^{\circ} )}{\frac{s i n ( 15 0 ^{\circ} ) - s i n ( 9 0 ^{\circ} )}{2} + tan ( 4 5 ^{\circ} )}

化简

= \frac{2 sin ( 12 0 ^{\circ} )}{sin ( 15 0 ^{\circ} ) - sin ( 9 0 ^{\circ} ) + 2 tan ( 4 5 ^{\circ} )}

使用以下普通恒等式:

sin (12 0^{\circ}) = \frac{3}{2}

sin (12 0^{\circ})

sin (x)

周期表（周期为

36 0^{\circ} n

"）：

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= \frac{3}{2}

使用以下普通恒等式:

sin (15 0^{\circ}) = \frac{1}{2}

sin (15 0^{\circ})

sin (x)

周期表（周期为

36 0^{\circ} n

"）：

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= \frac{1}{2}

使用以下普通恒等式:

sin (9 0^{\circ}) = 1

sin (9 0^{\circ})

sin (x)

周期表（周期为

36 0^{\circ} n

"）：

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} sin (x) 0 \frac{1}{2} \frac{2}{2} \frac{3}{2} 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} sin (x) 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2}

= 1

使用以下普通恒等式:

tan (4 5^{\circ}) = 1

tan (4 5^{\circ})

tan (x)

周期表（周期为

18 0^{\circ} n

）：

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} tan (x) 0 \frac{3}{3} 13 \pm \infty - 3 - 1 - \frac{3}{3}

= 1

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

化简

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

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

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

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

数字相乘:

2 \cdot 1 = 2

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

数字相加/相减:

- 1 + 2 = 1

= \frac{1}{2} + 1

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

化简

\frac{1}{2} + 1 : \frac{3}{2}

\frac{1}{2} + 1

将项转换为分式:

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

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

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{1 + 1 \cdot 2}{2}

1 + 1 \cdot 2 = 3

1 + 1 \cdot 2

数字相乘:

1 \cdot 2 = 2

= 1 + 2

数字相加:

1 + 2 = 3

= 3

= \frac{3}{2}

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

乘

2 \cdot \frac{3}{2} : 3

2 \cdot \frac{3}{2}

分式相乘:

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

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

约分:

2

= 3

= \frac{3}{\frac{3}{2}}

使用分式法则:

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

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

= \frac{2 3}{3}

流行的例子

arccos (- \frac{1}{8})

10.3 sin (3 7^{\circ})

2sin^2((3pi)/2)

2 sin^{2} (\frac{3 π}{2})

sin (- 1 (- 1))

2arctan(sqrt(3))

2 arctan (3)