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受欢迎的三角函数 >

(1/2 sin(2x))^2= 1/4 sin^2(4x)

解答

(\frac{1}{2} sin (2 x))^{2} = \frac{1}{4} sin^{2} (4 x)

解答

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

+1

度数

x = 0^{\circ} + 12 0^{\circ} n, x = 6 0^{\circ} + 12 0^{\circ} n, x = 3 0^{\circ} + 12 0^{\circ} n, x = 9 0^{\circ} + 12 0^{\circ} n

求解步骤

(\frac{1}{2} sin (2 x))^{2} = \frac{1}{4} sin^{2} (4 x)

两边减去

\frac{1}{4} sin^{2} (4 x)

\frac{1}{4} sin^{2} (2 x) - \frac{1}{4} sin^{2} (4 x) = 0

化简

\frac{1}{4} sin^{2} (2 x) - \frac{1}{4} sin^{2} (4 x) : \frac{sin ^{2} ( 2 x ) - sin ^{2} ( 4 x )}{4}

\frac{1}{4} sin^{2} (2 x) - \frac{1}{4} sin^{2} (4 x)

\frac{1}{4} sin^{2} (2 x) = \frac{sin ^{2} ( 2 x )}{4}

\frac{1}{4} sin^{2} (2 x)

分式相乘:

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

= \frac{1 \cdot sin ^{2} ( 2 x )}{4}

乘以:

1 \cdot sin^{2} (2 x) = sin^{2} (2 x)

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

\frac{1}{4} sin^{2} (4 x) = \frac{sin ^{2} ( 4 x )}{4}

\frac{1}{4} sin^{2} (4 x)

分式相乘:

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

= \frac{1 \cdot sin ^{2} ( 4 x )}{4}

乘以:

1 \cdot sin^{2} (4 x) = sin^{2} (4 x)

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

= \frac{sin ^{2} ( 2 x )}{4} - \frac{sin ^{2} ( 4 x )}{4}

使用法则

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

= \frac{sin ^{2} ( 2 x ) - sin ^{2} ( 4 x )}{4}

\frac{sin ^{2} ( 2 x ) - sin ^{2} ( 4 x )}{4} = 0

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

sin^{2} (2 x) - sin^{2} (4 x) = 0

分解

sin^{2} (2 x) - sin^{2} (4 x) : (sin (2 x) + sin (4 x)) (sin (2 x) - sin (4 x))

sin^{2} (2 x) - sin^{2} (4 x)

使用平方差公式:

x^{2} - y^{2} = (x + y) (x - y)

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

= (sin (2 x) + sin (4 x)) (sin (2 x) - sin (4 x))

(sin (2 x) + sin (4 x)) (sin (2 x) - sin (4 x)) = 0

分别求解每个部分

sin (2 x) + sin (4 x) = 0 or sin (2 x) - sin (4 x) = 0

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

sin (2 x) + sin (4 x) = 0

使用三角恒等式改写

sin (2 x) + sin (4 x)

使用和差化积恒等式:

sin (s) + sin (t) = 2 sin (\frac{s + t}{2}) cos (\frac{s - t}{2})

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

化简

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

2 sin (\frac{2 x + 4 x}{2}) cos (\frac{2 x - 4 x}{2})

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

\frac{2 x + 4 x}{2}

同类项相加:

2 x + 4 x = 6 x

= \frac{6 x}{2}

数字相除:

\frac{6}{2} = 3

= 3 x

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

\frac{2 x - 4 x}{2} = - x

\frac{2 x - 4 x}{2}

同类项相加:

2 x - 4 x = - 2 x

= \frac{- 2 x}{2}

使用分式法则:

\frac{- a}{b} = - \frac{a}{b}

= - \frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= - x

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

使用负角恒等式:

cos (- x) = cos (x)

= 2 cos (x) sin (3 x)

= 2 cos (x) sin (3 x)

2 cos (x) sin (3 x) = 0

分别求解每个部分

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

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

sin (3 x) = 0

sin (3 x) = 0

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}

3 x = 0 + 2 πn, 3 x = π + 2 πn

3 x = 0 + 2 πn, 3 x = π + 2 πn

解

3 x = 0 + 2 πn : x = \frac{2 πn}{3}

3 x = 0 + 2 πn

0 + 2 πn = 2 πn

3 x = 2 πn

两边除以

3

3 x = 2 πn

两边除以

3

\frac{3 x}{3} = \frac{2 πn}{3}

化简

x = \frac{2 πn}{3}

x = \frac{2 πn}{3}

解

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

3 x = π + 2 πn

两边除以

3

3 x = π + 2 πn

两边除以

3

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

化简

x = \frac{π}{3} + \frac{2 πn}{3}

x = \frac{π}{3} + \frac{2 πn}{3}

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

合并所有解

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

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

sin (2 x) - sin (4 x) = 0

使用三角恒等式改写

sin (2 x) - sin (4 x)

使用和差化积恒等式:

sin (s) - sin (t) = 2 sin (\frac{s - t}{2}) cos (\frac{s + t}{2})

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

化简

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

2 sin (\frac{2 x - 4 x}{2}) cos (\frac{2 x + 4 x}{2})

\frac{2 x - 4 x}{2} = - x

\frac{2 x - 4 x}{2}

同类项相加:

2 x - 4 x = - 2 x

= \frac{- 2 x}{2}

使用分式法则:

\frac{- a}{b} = - \frac{a}{b}

= - \frac{2 x}{2}

数字相除:

\frac{2}{2} = 1

= - x

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

使用负角恒等式:

sin (- x) = - sin (x)

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

去除括号:

(- a) = - a

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

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

\frac{2 x + 4 x}{2}

同类项相加:

2 x + 4 x = 6 x

= \frac{6 x}{2}

数字相除:

\frac{6}{2} = 3

= 3 x

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

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

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

分别求解每个部分

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

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

cos (3 x) = 0

cos (3 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}

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

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

解

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

3 x = \frac{π}{2} + 2 πn

两边除以

3

3 x = \frac{π}{2} + 2 πn

两边除以

3

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

化简

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

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

\frac{\frac{π}{2}}{3} = \frac{π}{6}

\frac{\frac{π}{2}}{3}

使用分式法则:

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

= \frac{π}{2 \cdot 3}

数字相乘:

2 \cdot 3 = 6

= \frac{π}{6}

= \frac{π}{6} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}

x = \frac{π}{6} + \frac{2 πn}{3}

解

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

3 x = \frac{3 π}{2} + 2 πn

两边除以

3

3 x = \frac{3 π}{2} + 2 πn

两边除以

3

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

化简

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

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

\frac{\frac{3 π}{2}}{3} = \frac{π}{2}

\frac{\frac{3 π}{2}}{3}

使用分式法则:

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

= \frac{3 π}{2 \cdot 3}

数字相乘:

2 \cdot 3 = 6

= \frac{3 π}{6}

约分:

3

= \frac{π}{2}

= \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{2} + \frac{2 πn}{3}

x = \frac{π}{2} + \frac{2 πn}{3}

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

sin (x) = 0 : x = 2 πn, x = π + 2 πn

sin (x) = 0

sin (x) = 0

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}

x = 0 + 2 πn, x = π + 2 πn

x = 0 + 2 πn, x = π + 2 πn

解

x = 0 + 2 πn : x = 2 πn

x = 0 + 2 πn

0 + 2 πn = 2 πn

x = 2 πn

x = 2 πn, x = π + 2 πn

合并所有解

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

合并所有解

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

合并重叠的区间

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

作图

流行的例子

8sin^2(x)-3sin(x)-2=0

8 sin^{2} (x) - 3 sin (x) - 2 = 0

6 sin (x) + 12 = 15

cot^2(x)cos(x)=cos(x)

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

1+2cos(x)+cos^2(x)=3sin^2(x)

1 + 2 cos (x) + cos^{2} (x) = 3 sin^{2} (x)

solvefor L,sin(kL)=0

so l v e f or L, sin (k L) = 0