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受欢迎的三角函数 >

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

解答

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

解答

x = 2 πn, x = π + 2 πn, x = - 0.32175 \dots + πn

+1

度数

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = - 18.43494 \dots^{\circ} + 18 0^{\circ} n

求解步骤

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

分解

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

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

使用指数法则:

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

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

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

因式分解出通项

sin (x)

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

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

分别求解每个部分

sin (x) = 0 or 3 sin (x) + 2 cos^{2} (\frac{x}{2}) - 1 = 0

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

3 sin (x) + 2 cos^{2} (\frac{x}{2}) - 1 = 0 : x = arctan (- \frac{1}{3}) + πn

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

使用三角恒等式改写

- 1 + 2 cos^{2} (\frac{x}{2}) + 3 sin (x)

使用倍角公式:

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

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

乘

2 \cdot \frac{x}{2} : x

2 \cdot \frac{x}{2}

分式相乘:

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

= \frac{x \cdot 2}{2}

约分:

2

= x

= 3 sin (x) + cos (x)

在两边除以

cos (x), cos (x) \neq = 0

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

化简

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

使用基本三角恒等式:

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

1 + 3 tan (x) = 0

1 + 3 tan (x) = 0

将

1

到右边

1 + 3 tan (x) = 0

两边减去

1

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

化简

3 tan (x) = - 1

3 tan (x) = - 1

两边除以

3

3 tan (x) = - 1

两边除以

3

\frac{3 tan ( x )}{3} = \frac{- 1}{3}

化简

tan (x) = - \frac{1}{3}

tan (x) = - \frac{1}{3}

使用反三角函数性质

tan (x) = - \frac{1}{3}

tan (x) = - \frac{1}{3}

的通解

tan (x) = - a \Rightarrow x = arctan (- a) + πn

x = arctan (- \frac{1}{3}) + πn

x = arctan (- \frac{1}{3}) + πn

合并所有解

x = 2 πn, x = π + 2 πn, x = arctan (- \frac{1}{3}) + πn

以小数形式表示解

x = 2 πn, x = π + 2 πn, x = - 0.32175 \dots + πn

作图

流行的例子

3tan^2(y)=5sec(y)-1

3 tan^{2} (y) = 5 sec (y) - 1

((1-tan^2(a)))/((tan(a)))=2cot^2(a)

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cos(6x)=cos(2x)

cos (6 x) = cos (2 x)

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

cos^4(x)+cos^3(x)-2=0

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