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受欢迎的三角函数 >

cos(2x)cos(x)-sin(2x)sin(x)=-(sqrt(3))/2

解答

cos (2 x) cos (x) - sin (2 x) sin (x) = - \frac{3}{2}

解答

x = \frac{5 π}{18} + \frac{2 πn}{3}, x = \frac{7 π}{18} + \frac{2 πn}{3}

+1

度数

x = 5 0^{\circ} + 12 0^{\circ} n, x = 7 0^{\circ} + 12 0^{\circ} n

求解步骤

cos (2 x) cos (x) - sin (2 x) sin (x) = - \frac{3}{2}

使用三角恒等式改写

cos (2 x) cos (x) - sin (2 x) sin (x)

使用角和恒等式:

cos (s) cos (t) - sin (s) sin (t) = cos (s + t)

= cos (2 x + x)

cos (2 x + x) = - \frac{3}{2}

cos (2 x + x) = - \frac{3}{2}

的通解

cos (x)

周期表（周期为

2 πn

）：

x 0 \frac{π}{6} \frac{π}{4} \frac{π}{3} \frac{π}{2} \frac{2 π}{3} \frac{3 π}{4} \frac{5 π}{6} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x π \frac{7 π}{6} \frac{5 π}{4} \frac{4 π}{3} \frac{3 π}{2} \frac{5 π}{3} \frac{7 π}{4} \frac{11 π}{6} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

2 x + x = \frac{5 π}{6} + 2 πn, 2 x + x = \frac{7 π}{6} + 2 πn

2 x + x = \frac{5 π}{6} + 2 πn, 2 x + x = \frac{7 π}{6} + 2 πn

解

2 x + x = \frac{5 π}{6} + 2 πn : x = \frac{5 π}{18} + \frac{2 πn}{3}

2 x + x = \frac{5 π}{6} + 2 πn

同类项相加:

2 x + x = 3 x

3 x = \frac{5 π}{6} + 2 πn

两边除以

3

3 x = \frac{5 π}{6} + 2 πn

两边除以

3

\frac{3 x}{3} = \frac{\frac{5 π}{6}}{3} + \frac{2 πn}{3}

化简

\frac{3 x}{3} = \frac{\frac{5 π}{6}}{3} + \frac{2 πn}{3}

化简

\frac{3 x}{3} : x

\frac{3 x}{3}

数字相除:

\frac{3}{3} = 1

= x

化简

\frac{\frac{5 π}{6}}{3} + \frac{2 πn}{3} : \frac{5 π}{18} + \frac{2 πn}{3}

\frac{\frac{5 π}{6}}{3} + \frac{2 πn}{3}

\frac{\frac{5 π}{6}}{3} = \frac{5 π}{18}

\frac{\frac{5 π}{6}}{3}

使用分式法则:

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

= \frac{5 π}{6 \cdot 3}

数字相乘:

6 \cdot 3 = 18

= \frac{5 π}{18}

= \frac{5 π}{18} + \frac{2 πn}{3}

x = \frac{5 π}{18} + \frac{2 πn}{3}

x = \frac{5 π}{18} + \frac{2 πn}{3}

x = \frac{5 π}{18} + \frac{2 πn}{3}

解

2 x + x = \frac{7 π}{6} + 2 πn : x = \frac{7 π}{18} + \frac{2 πn}{3}

2 x + x = \frac{7 π}{6} + 2 πn

同类项相加:

2 x + x = 3 x

3 x = \frac{7 π}{6} + 2 πn

两边除以

3

3 x = \frac{7 π}{6} + 2 πn

两边除以

3

\frac{3 x}{3} = \frac{\frac{7 π}{6}}{3} + \frac{2 πn}{3}

化简

\frac{3 x}{3} = \frac{\frac{7 π}{6}}{3} + \frac{2 πn}{3}

化简

\frac{3 x}{3} : x

\frac{3 x}{3}

数字相除:

\frac{3}{3} = 1

= x

化简

\frac{\frac{7 π}{6}}{3} + \frac{2 πn}{3} : \frac{7 π}{18} + \frac{2 πn}{3}

\frac{\frac{7 π}{6}}{3} + \frac{2 πn}{3}

\frac{\frac{7 π}{6}}{3} = \frac{7 π}{18}

\frac{\frac{7 π}{6}}{3}

使用分式法则:

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

= \frac{7 π}{6 \cdot 3}

数字相乘:

6 \cdot 3 = 18

= \frac{7 π}{18}

= \frac{7 π}{18} + \frac{2 πn}{3}

x = \frac{7 π}{18} + \frac{2 πn}{3}

x = \frac{7 π}{18} + \frac{2 πn}{3}

x = \frac{7 π}{18} + \frac{2 πn}{3}

x = \frac{5 π}{18} + \frac{2 πn}{3}, x = \frac{7 π}{18} + \frac{2 πn}{3}

作图

流行的例子

sec(θ)=tan(θ)+cot(θ)

sec (θ) = tan (θ) + cot (θ)

sec^2(x)= 4/3 ,0<= x<= 2pi

sec^{2} (x) = \frac{4}{3}, 0 \leq x \leq 2 π

sqrt(3)tan(3θ)-1=0

3 tan (3 θ) - 1 = 0

2 tan (x) = sec (x)

cos (x) = 2 π