cos(b)= 38/70

解答

cos (b) = \frac{38}{70}

b = 0.99696 \dots + 2 πn, b = 2 π - 0.99696 \dots + 2 πn

度数

b = 57.12165 \dots^{\circ} + 36 0^{\circ} n, b = 302.87834 \dots^{\circ} + 36 0^{\circ} n

求解步骤

cos (b) = \frac{38}{70}

约分:

2

cos (b) = \frac{19}{35}

使用反三角函数性质

cos (b) = \frac{19}{35}

cos (b) = \frac{19}{35}

的通解

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

b = arccos (\frac{19}{35}) + 2 πn, b = 2 π - arccos (\frac{19}{35}) + 2 πn

b = arccos (\frac{19}{35}) + 2 πn, b = 2 π - arccos (\frac{19}{35}) + 2 πn

以小数形式表示解

b = 0.99696 \dots + 2 πn, b = 2 π - 0.99696 \dots + 2 πn

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

3 sin (x) - 4 sin^{3} (x) = 1 - 2 sin^{2} (x)

sin^{2} (a) = \frac{( 2 tan ( a ) )}{( 1 + tan ^{2} ( a ) )}

\frac{tan ( a )}{2} = \frac{2}{11}

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