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受欢迎的三角函数 >

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

解答

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

解答

x = 2 πn, x = π + 2 πn

+1

度数

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n

求解步骤

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

分解

sin^{3} (x) cos (x) - sin^{2} (x) : sin^{2} (x) (sin (x) cos (x) - 1)

sin^{3} (x) cos (x) - sin^{2} (x)

使用指数法则:

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

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

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

因式分解出通项

sin^{2} (x)

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

sin^{2} (x) (sin (x) cos (x) - 1) = 0

分别求解每个部分

sin^{2} (x) = 0 or sin (x) cos (x) - 1 = 0

sin^{2} (x) = 0 : x = 2 πn, x = π + 2 πn

sin^{2} (x) = 0

使用法则

x^{n} = 0 \Rightarrow x = 0

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

sin (x) cos (x) - 1 = 0 :

无解

sin (x) cos (x) - 1 = 0

使用三角恒等式改写

sin (x) cos (x) - 1

使用倍角公式:

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

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

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

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

将

1

到右边

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

两边加上

1

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

化简

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

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

在两边乘以

2

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

在两边乘以

2

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

化简

sin (2 x) = 2

sin (2 x) = 2

- 1 \leq sin (x) \leq 1

无解

合并所有解

x = 2 πn, x = π + 2 πn

作图

流行的例子

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

cos^2(45-a)-sin^2(45-a)=sin^2(a)

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

cos^2(x)cos(x)=0