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受欢迎的三角函数 >

sin^2(210)

解答

sin^{2} (21 0^{\circ})

解答

\frac{1}{4}

+1

十进制

0.25

求解步骤

sin^{2} (21 0^{\circ})

使用三角恒等式改写:

\frac{1 - cos ( 6 0 ^{\circ} )}{2}

sin^{2} (21 0^{\circ})

利用以下特性:

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

使用倍角公式

cos (2 θ) = 1 - 2 sin^{2} (θ)

交换两边

2 sin^{2} (θ) - 1 = - cos (2 θ)

两边加上

1

2 sin^{2} (θ) = 1 - cos (2 θ)

两边除以

2

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

= \frac{1 - cos ( 2 \cdot 21 0 ^{\circ} )}{2}

化简

= \frac{1 - cos ( 42 0 ^{\circ} )}{2}

cos (42 0^{\circ}) = cos (6 0^{\circ})

cos (42 0^{\circ})

将

42 0^{\circ}

改写为

36 0^{\circ} + 6 0^{\circ}

= cos (36 0^{\circ} + 6 0^{\circ})

使用周期

cos

:

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

cos (36 0^{\circ} + 6 0^{\circ}) = cos (6 0^{\circ})

= cos (6 0^{\circ})

= \frac{1 - cos ( 6 0 ^{\circ} )}{2}

= \frac{1 - cos ( 6 0 ^{\circ} )}{2}

使用以下普通恒等式:

cos (6 0^{\circ}) = \frac{1}{2}

cos (6 0^{\circ})

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

= \frac{1}{2}

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

化简

\frac{1 - \frac{1}{2}}{2} : \frac{1}{4}

\frac{1 - \frac{1}{2}}{2}

化简

1 - \frac{1}{2} : \frac{1}{2}

1 - \frac{1}{2}

将项转换为分式:

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

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

1 \cdot 2 - 1 = 1

1 \cdot 2 - 1

数字相乘:

1 \cdot 2 = 2

= 2 - 1

数字相减:

2 - 1 = 1

= 1

= \frac{1}{2}

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

使用分式法则:

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

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

数字相乘:

2 \cdot 2 = 4

= \frac{1}{4}

= \frac{1}{4}

流行的例子

sin (4 5^{\circ}) cos (4 5^{\circ})

sin (23 0^{\circ})

csc (5 0^{\circ})

cos (\frac{7}{6} π)

sec(-(7pi)/(12))

sec (- \frac{7 π}{12})