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

解答

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

解答

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

+1

度数

x = 9 0^{\circ} + 36 0^{\circ} n, x = 27 0^{\circ} + 36 0^{\circ} n, x = 12 0^{\circ} + 18 0^{\circ} n, x = 15 0^{\circ} + 18 0^{\circ} n

求解步骤

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

两边减去

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

2 cos^{2} (x) sin (x) + \frac{3}{2} cos (x) = 0

化简

2 cos^{2} (x) sin (x) + \frac{3}{2} cos (x) : \frac{4 cos ^{2} ( x ) sin ( x ) + 3 cos ( x )}{2}

2 cos^{2} (x) sin (x) + \frac{3}{2} cos (x)

乘

\frac{3}{2} cos (x) : \frac{3 cos ( x )}{2}

\frac{3}{2} cos (x)

分式相乘:

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

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

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

将项转换为分式:

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

= \frac{2 cos ^{2} ( x ) sin ( x ) \cdot 2}{2} + \frac{3 cos ( x )}{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{2 cos ^{2} ( x ) sin ( x ) \cdot 2 + 3 cos ( x )}{2}

数字相乘:

2 \cdot 2 = 4

= \frac{4 cos ^{2} ( x ) sin ( x ) + 3 cos ( x )}{2}

\frac{4 cos ^{2} ( x ) sin ( x ) + 3 cos ( x )}{2} = 0

\frac{f ( x )}{g ( x )} = 0 \Rightarrow f (x) = 0

4 cos^{2} (x) sin (x) + 3 cos (x) = 0

分解

4 cos^{2} (x) sin (x) + 3 cos (x) : cos (x) (4 cos (x) sin (x) + 3)

4 cos^{2} (x) sin (x) + 3 cos (x)

使用指数法则:

a^{b + c} = a^{b} a^{c}

cos^{2} (x) = cos (x) cos (x)

= 4 cos (x) cos (x) sin (x) + 3 cos (x)

因式分解出通项

cos (x)

= cos (x) (4 cos (x) sin (x) + 3)

cos (x) (4 cos (x) sin (x) + 3) = 0

分别求解每个部分

cos (x) = 0 or 4 cos (x) sin (x) + 3 = 0

cos (x) = 0 : x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn

cos (x) = 0

cos (x) = 0

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}

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

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

4 cos (x) sin (x) + 3 = 0 : x = \frac{2 π}{3} + πn, x = \frac{5 π}{6} + πn

4 cos (x) sin (x) + 3 = 0

使用三角恒等式改写

4 cos (x) sin (x) + 3

使用倍角公式:

2 sin (x) cos (x) = sin (2 x)

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

= 3 + 4 \cdot \frac{sin ( 2 x )}{2}

3 + 4 \cdot \frac{sin ( 2 x )}{2} = 0

4 \cdot \frac{sin ( 2 x )}{2} = 2 sin (2 x)

4 \cdot \frac{sin ( 2 x )}{2}

分式相乘:

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

= \frac{sin ( 2 x ) \cdot 4}{2}

数字相除:

\frac{4}{2} = 2

= 2 sin (2 x)

3 + 2 sin (2 x) = 0

将

3

到右边

3 + 2 sin (2 x) = 0

两边减去

3

3 + 2 sin (2 x) - 3 = 0 - 3

化简

2 sin (2 x) = - 3

2 sin (2 x) = - 3

两边除以

2

2 sin (2 x) = - 3

两边除以

2

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

化简

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

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

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

的通解

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

2 x = \frac{4 π}{3} + 2 πn, 2 x = \frac{5 π}{3} + 2 πn

2 x = \frac{4 π}{3} + 2 πn, 2 x = \frac{5 π}{3} + 2 πn

解

2 x = \frac{4 π}{3} + 2 πn : x = \frac{2 π}{3} + πn

2 x = \frac{4 π}{3} + 2 πn

两边除以

2

2 x = \frac{4 π}{3} + 2 πn

两边除以

2

\frac{2 x}{2} = \frac{\frac{4 π}{3}}{2} + \frac{2 πn}{2}

化简

\frac{2 x}{2} = \frac{\frac{4 π}{3}}{2} + \frac{2 πn}{2}

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

\frac{\frac{4 π}{3}}{2} + \frac{2 πn}{2} : \frac{2 π}{3} + πn

\frac{\frac{4 π}{3}}{2} + \frac{2 πn}{2}

\frac{\frac{4 π}{3}}{2} = \frac{2 π}{3}

\frac{\frac{4 π}{3}}{2}

使用分式法则:

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

= \frac{4 π}{3 \cdot 2}

数字相乘:

3 \cdot 2 = 6

= \frac{4 π}{6}

约分:

2

= \frac{2 π}{3}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

数字相除:

\frac{2}{2} = 1

= πn

= \frac{2 π}{3} + πn

x = \frac{2 π}{3} + πn

x = \frac{2 π}{3} + πn

x = \frac{2 π}{3} + πn

解

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

2 x = \frac{5 π}{3} + 2 πn

两边除以

2

2 x = \frac{5 π}{3} + 2 πn

两边除以

2

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

化简

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

化简

\frac{2 x}{2} : x

\frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= x

化简

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

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

\frac{\frac{5 π}{3}}{2} = \frac{5 π}{6}

\frac{\frac{5 π}{3}}{2}

使用分式法则:

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

= \frac{5 π}{3 \cdot 2}

数字相乘:

3 \cdot 2 = 6

= \frac{5 π}{6}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

数字相除:

\frac{2}{2} = 1

= πn

= \frac{5 π}{6} + πn

x = \frac{5 π}{6} + πn

x = \frac{5 π}{6} + πn

x = \frac{5 π}{6} + πn

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

合并所有解

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

流行的例子

4 sin (x^{\circ}) + 1 = - 2

(2cos(x)+1)(sqrt(3)tan(x)-1)=0

(2 cos (x) + 1) (3 tan (x) - 1) = 0

solvefor α,cos^2(α)+cos^2(β)=1 求解

α, cos^{2} (α) + cos^{2} (β) = 1

sin^2(x)-cos(x)tan(x)=0

sin^{2} (x) - cos (x) tan (x) = 0

sin (x + 3 0^{\circ}) = \frac{1}{2}