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受欢迎的三角函数 >

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

解答

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

解答

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

+1

度数

x = 18 0^{\circ} + 36 0^{\circ} n, x = 3 0^{\circ} + 36 0^{\circ} n, x = 15 0^{\circ} + 36 0^{\circ} n

求解步骤

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

两边减去

sin^{2} (x)

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

使用三角恒等式改写

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

使用毕达哥拉斯恒等式:

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

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

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

化简

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

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

- (1 - cos^{2} (x)) : - 1 + cos^{2} (x)

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

打开括号

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

使用加减运算法则

- (- a) = a, - (a) = - a

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

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

乘开

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

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

使用 FOIL 方法:

(a + b) (c + d) = a c + a d + b c + b d

a = - cos (x), b = 2 sin (x), c = 1, d = cos (x)

= (- cos (x)) \cdot 1 + (- cos (x)) cos (x) + 2 sin (x) \cdot 1 + 2 sin (x) cos (x)

使用加减运算法则

+ (- a) = - a

= - 1 \cdot cos (x) - cos (x) cos (x) + 2 \cdot 1 \cdot sin (x) + 2 sin (x) cos (x)

化简

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

- 1 \cdot cos (x) - cos (x) cos (x) + 2 \cdot 1 \cdot sin (x) + 2 sin (x) cos (x)

1 \cdot cos (x) = cos (x)

1 \cdot cos (x)

乘以:

1 \cdot cos (x) = cos (x)

= cos (x)

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

cos (x) cos (x)

使用指数法则:

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

cos (x) cos (x) = cos^{1 + 1} (x)

= cos^{1 + 1} (x)

数字相加:

1 + 1 = 2

= cos^{2} (x)

2 \cdot 1 \cdot sin (x) = 2 sin (x)

2 \cdot 1 \cdot sin (x)

数字相乘:

2 \cdot 1 = 2

= 2 sin (x)

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

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

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

化简

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

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

对同类项分组

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

同类项相加:

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

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

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

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

- 1 - cos (x) + 2 sin (x) + 2 cos (x) sin (x) = 0

分解

- 1 - cos (x) + 2 sin (x) + 2 cos (x) sin (x) : (cos (x) + 1) (2 sin (x) - 1)

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

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

从

2 sin (x) cos (x) + 2 sin (x)

分解出因式

2 sin (x)

:

2 sin (x) (cos (x) + 1)

2 sin (x) cos (x) + 2 sin (x)

因式分解出通项

2 sin (x)

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

从

- cos (x) - 1

分解出因式

- 1

:

- (cos (x) + 1)

- cos (x) - 1

因式分解出通项

- 1

= - (cos (x) + 1)

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

因式分解出通项

cos (x) + 1

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

(cos (x) + 1) (2 sin (x) - 1) = 0

分别求解每个部分

cos (x) + 1 = 0 or 2 sin (x) - 1 = 0

cos (x) + 1 = 0 : x = π + 2 πn

cos (x) + 1 = 0

将

1

到右边

cos (x) + 1 = 0

两边减去

1

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

化简

cos (x) = - 1

cos (x) = - 1

cos (x) = - 1

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 = π + 2 πn

x = π + 2 πn

2 sin (x) - 1 = 0 : x = \frac{π}{6} + 2 πn, x = \frac{5 π}{6} + 2 πn

2 sin (x) - 1 = 0

将

1

到右边

2 sin (x) - 1 = 0

两边加上

1

2 sin (x) - 1 + 1 = 0 + 1

化简

2 sin (x) = 1

2 sin (x) = 1

两边除以

2

2 sin (x) = 1

两边除以

2

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

化简

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

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

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

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

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

合并所有解

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

作图

流行的例子

sec^2(x)+2tan^2(x)=2

sec^{2} (x) + 2 tan^{2} (x) = 2

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

8sin^2(x)+4cos^2(x)=7

8 sin^{2} (x) + 4 cos^{2} (x) = 7

10cos^2(x)+cos(x)=11sin^2(x)-9

10 cos^{2} (x) + cos (x) = 11 sin^{2} (x) - 9

sin(6.5x+2.5)=0.0851

sin (6.5 x + 2.5) = 0.0851