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受欢迎的三角函数 >

cos(2B)= 21/35

解答

cos (2 B) = \frac{21}{35}

解答

B = \frac{0.92729 \dots}{2} + πn, B = π - \frac{0.92729 \dots}{2} + πn

+1

度数

B = 26.56505 \dots^{\circ} + 18 0^{\circ} n, B = 153.43494 \dots^{\circ} + 18 0^{\circ} n

求解步骤

cos (2 B) = \frac{21}{35}

约分:

7

cos (2 B) = \frac{3}{5}

使用反三角函数性质

cos (2 B) = \frac{3}{5}

cos (2 B) = \frac{3}{5}

的通解

cos (x) = a \Rightarrow x = arccos (a) + 2 πn, x = 2 π - arccos (a) + 2 πn

2 B = arccos (\frac{3}{5}) + 2 πn, 2 B = 2 π - arccos (\frac{3}{5}) + 2 πn

2 B = arccos (\frac{3}{5}) + 2 πn, 2 B = 2 π - arccos (\frac{3}{5}) + 2 πn

解

2 B = arccos (\frac{3}{5}) + 2 πn : B = \frac{arccos ( \frac{3}{5} )}{2} + πn

2 B = arccos (\frac{3}{5}) + 2 πn

两边除以

2

2 B = arccos (\frac{3}{5}) + 2 πn

两边除以

2

\frac{2 B}{2} = \frac{arccos ( \frac{3}{5} )}{2} + \frac{2 πn}{2}

化简

B = \frac{arccos ( \frac{3}{5} )}{2} + πn

B = \frac{arccos ( \frac{3}{5} )}{2} + πn

解

2 B = 2 π - arccos (\frac{3}{5}) + 2 πn : B = π - \frac{arccos ( \frac{3}{5} )}{2} + πn

2 B = 2 π - arccos (\frac{3}{5}) + 2 πn

两边除以

2

2 B = 2 π - arccos (\frac{3}{5}) + 2 πn

两边除以

2

\frac{2 B}{2} = \frac{2 π}{2} - \frac{arccos ( \frac{3}{5} )}{2} + \frac{2 πn}{2}

化简

B = π - \frac{arccos ( \frac{3}{5} )}{2} + πn

B = π - \frac{arccos ( \frac{3}{5} )}{2} + πn

B = \frac{arccos ( \frac{3}{5} )}{2} + πn, B = π - \frac{arccos ( \frac{3}{5} )}{2} + πn

以小数形式表示解

B = \frac{0.92729 \dots}{2} + πn, B = π - \frac{0.92729 \dots}{2} + πn

作图

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