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sin^3(o)=4sin(o)sin^2(o)sin^4(o)

解答

sin^{3} (o) = 4 sin (o) sin^{2} (o) sin^{4} (o)

解答

o = 2 πn, o = π + 2 πn, o = \frac{5 π}{4} + 2 πn, o = \frac{7 π}{4} + 2 πn, o = \frac{π}{4} + 2 πn, o = \frac{3 π}{4} + 2 πn

+1

度数

o = 0^{\circ} + 36 0^{\circ} n, o = 18 0^{\circ} + 36 0^{\circ} n, o = 22 5^{\circ} + 36 0^{\circ} n, o = 31 5^{\circ} + 36 0^{\circ} n, o = 4 5^{\circ} + 36 0^{\circ} n, o = 13 5^{\circ} + 36 0^{\circ} n

求解步骤

sin^{3} (o) = 4 sin (o) sin^{2} (o) sin^{4} (o)

用替代法求解

sin^{3} (o) = 4 sin (o) sin^{2} (o) sin^{4} (o)

令

: sin (o) = u

u^{3} = 4 u u^{2} u^{4}

u^{3} = 4 u u^{2} u^{4} : u = 0, u = i \frac{1}{2}, u = - i \frac{1}{2}, u = - \frac{2}{2}, u = \frac{2}{2}

u^{3} = 4 u u^{2} u^{4}

交换两边

4 u u^{2} u^{4} = u^{3}

将

u^{3}

para o lado esquerdo

4 u u^{2} u^{4} = u^{3}

两边减去

u^{3}

4 u u^{2} u^{4} - u^{3} = u^{3} - u^{3}

化简

4 u^{7} - u^{3} = 0

4 u^{7} - u^{3} = 0

因式分解

4 u^{7} - u^{3} : u^{3} (2 u^{2} + 1) (2 u + 1) (2 u - 1)

4 u^{7} - u^{3}

因式分解出通项

u^{3} : u^{3} (4 u^{4} - 1)

4 u^{7} - u^{3}

使用指数法则:

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

u^{7} = u^{4} u^{3}

= 4 u^{4} u^{3} - u^{3}

因式分解出通项

u^{3}

= u^{3} (4 u^{4} - 1)

= u^{3} (4 u^{4} - 1)

分解

4 u^{4} - 1 : (2 u^{2} + 1) (2 u + 1) (2 u - 1)

4 u^{4} - 1

将

4 u^{4} - 1

改写为

(2 u^{2})^{2} - 1^{2}

4 u^{4} - 1

将

4

改写为

2^{2}

= 2^{2} u^{4} - 1

将

1

改写为

1^{2}

= 2^{2} u^{4} - 1^{2}

使用指数法则:

a^{b c} = (a^{b})^{c}

u^{4} = (u^{2})^{2}

= 2^{2} (u^{2})^{2} - 1^{2}

使用指数法则:

a^{m} b^{m} = (ab)^{m}

2^{2} (u^{2})^{2} = (2 u^{2})^{2}

= (2 u^{2})^{2} - 1^{2}

= (2 u^{2})^{2} - 1^{2}

使用平方差公式:

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

(2 u^{2})^{2} - 1^{2} = (2 u^{2} + 1) (2 u^{2} - 1)

= (2 u^{2} + 1) (2 u^{2} - 1)

分解

2 u^{2} - 1 : (2 u + 1) (2 u - 1)

2 u^{2} - 1

将

2 u^{2} - 1

改写为

(2 u)^{2} - 1^{2}

2 u^{2} - 1

使用根式运算法则:

a = (a)^{2}

2 = (2)^{2}

= (2)^{2} u^{2} - 1

将

1

改写为

1^{2}

= (2)^{2} u^{2} - 1^{2}

使用指数法则:

a^{m} b^{m} = (ab)^{m}

(2)^{2} u^{2} = (2 u)^{2}

= (2 u)^{2} - 1^{2}

= (2 u)^{2} - 1^{2}

使用平方差公式:

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

(2 u)^{2} - 1^{2} = (2 u + 1) (2 u - 1)

= (2 u + 1) (2 u - 1)

= (2 u^{2} + 1) (2 u + 1) (2 u - 1)

= u^{3} (2 u^{2} + 1) (2 u + 1) (2 u - 1)

u^{3} (2 u^{2} + 1) (2 u + 1) (2 u - 1) = 0

使用零因数法则： If

ab = 0

then

a = 0

or

b = 0

u = 0 or 2 u^{2} + 1 = 0 or 2 u + 1 = 0 or 2 u - 1 = 0

解

2 u^{2} + 1 = 0 : u = i \frac{1}{2}, u = - i \frac{1}{2}

2 u^{2} + 1 = 0

将

1

到右边

2 u^{2} + 1 = 0

两边减去

1

2 u^{2} + 1 - 1 = 0 - 1

化简

2 u^{2} = - 1

2 u^{2} = - 1

两边除以

2

2 u^{2} = - 1

两边除以

2

\frac{2 u ^{2}}{2} = \frac{- 1}{2}

化简

u^{2} = - \frac{1}{2}

u^{2} = - \frac{1}{2}

对于

x^{2} = f (a)

解为

x = f (a), - f (a)

u = - \frac{1}{2}, u = - - \frac{1}{2}

化简

- \frac{1}{2} : i \frac{1}{2}

- \frac{1}{2}

使用根式运算法则:

- a = - 1 a

- \frac{1}{2} = - 1 \frac{1}{2}

= - 1 \frac{1}{2}

使用虚数运算法则:

- 1 = i

= i \frac{1}{2}

化简

- - \frac{1}{2} : - i \frac{1}{2}

- - \frac{1}{2}

化简

- \frac{1}{2} : i \frac{1}{2}

- \frac{1}{2}

使用根式运算法则:

- a = - 1 a

- \frac{1}{2} = - 1 \frac{1}{2}

= - 1 \frac{1}{2}

使用虚数运算法则:

- 1 = i

= i \frac{1}{2}

= - i \frac{1}{2}

u = i \frac{1}{2}, u = - i \frac{1}{2}

解

2 u + 1 = 0 : u = - \frac{2}{2}

2 u + 1 = 0

将

1

到右边

2 u + 1 = 0

两边减去

1

2 u + 1 - 1 = 0 - 1

化简

2 u = - 1

2 u = - 1

两边除以

2

2 u = - 1

两边除以

2

\frac{2 u}{2} = \frac{- 1}{2}

化简

\frac{2 u}{2} = \frac{- 1}{2}

化简

\frac{2 u}{2} : u

\frac{2 u}{2}

约分:

2

= u

化简

\frac{- 1}{2} : - \frac{2}{2}

\frac{- 1}{2}

使用分式法则:

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

= - \frac{1}{2}

- \frac{1}{2}

有理化:

- \frac{2}{2}

- \frac{1}{2}

乘以共轭根式

\frac{2}{2}

= - \frac{1 \cdot 2}{2 2}

1 \cdot 2 = 2

22 = 2

22

使用根式运算法则:

a a = a

22 = 2

= 2

= - \frac{2}{2}

= - \frac{2}{2}

u = - \frac{2}{2}

u = - \frac{2}{2}

u = - \frac{2}{2}

解

2 u - 1 = 0 : u = \frac{2}{2}

2 u - 1 = 0

将

1

到右边

2 u - 1 = 0

两边加上

1

2 u - 1 + 1 = 0 + 1

化简

2 u = 1

2 u = 1

两边除以

2

2 u = 1

两边除以

2

\frac{2 u}{2} = \frac{1}{2}

化简

\frac{2 u}{2} = \frac{1}{2}

化简

\frac{2 u}{2} : u

\frac{2 u}{2}

约分:

2

= u

化简

\frac{1}{2} : \frac{2}{2}

\frac{1}{2}

乘以共轭根式

\frac{2}{2}

= \frac{1 \cdot 2}{2 2}

1 \cdot 2 = 2

22 = 2

22

使用根式运算法则:

a a = a

22 = 2

= 2

= \frac{2}{2}

u = \frac{2}{2}

u = \frac{2}{2}

u = \frac{2}{2}

解为

u = 0, u = i \frac{1}{2}, u = - i \frac{1}{2}, u = - \frac{2}{2}, u = \frac{2}{2}

u = sin (o)

代回

sin (o) = 0, sin (o) = i \frac{1}{2}, sin (o) = - i \frac{1}{2}, sin (o) = - \frac{2}{2}, sin (o) = \frac{2}{2}

sin (o) = 0, sin (o) = i \frac{1}{2}, sin (o) = - i \frac{1}{2}, sin (o) = - \frac{2}{2}, sin (o) = \frac{2}{2}

sin (o) = 0 : o = 2 πn, o = π + 2 πn

sin (o) = 0

sin (o) = 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}

o = 0 + 2 πn, o = π + 2 πn

o = 0 + 2 πn, o = π + 2 πn

解

o = 0 + 2 πn : o = 2 πn

o = 0 + 2 πn

0 + 2 πn = 2 πn

o = 2 πn

o = 2 πn, o = π + 2 πn

sin (o) = i \frac{1}{2} :

无解

sin (o) = i \frac{1}{2}

无解

sin (o) = - i \frac{1}{2} :

无解

sin (o) = - i \frac{1}{2}

无解

sin (o) = - \frac{2}{2} : o = \frac{5 π}{4} + 2 πn, o = \frac{7 π}{4} + 2 πn

sin (o) = - \frac{2}{2}

sin (o) = - \frac{2}{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}

o = \frac{5 π}{4} + 2 πn, o = \frac{7 π}{4} + 2 πn

o = \frac{5 π}{4} + 2 πn, o = \frac{7 π}{4} + 2 πn

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

sin (o) = \frac{2}{2}

sin (o) = \frac{2}{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}

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

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

合并所有解

o = 2 πn, o = π + 2 πn, o = \frac{5 π}{4} + 2 πn, o = \frac{7 π}{4} + 2 πn, o = \frac{π}{4} + 2 πn, o = \frac{3 π}{4} + 2 πn

流行的例子

cos^{2} (x) = - 4

8sin^4(x)-6sin^2(x)+1=0

8 sin^{4} (x) - 6 sin^{2} (x) + 1 = 0

4sin^2(x)+2cos(x)+a=3

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

cos^5(x)+cos(x)+4cos^2(x)=2

cos^{5} (x) + cos (x) + 4 cos^{2} (x) = 2

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

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