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受欢迎的三角函数 >

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

解答

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

解答

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn, x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

+1

度数

x = 9 0^{\circ} + 36 0^{\circ} n, x = 27 0^{\circ} + 36 0^{\circ} n, x = 21 0^{\circ} + 36 0^{\circ} n, x = 33 0^{\circ} + 36 0^{\circ} n

求解步骤

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

使用三角恒等式改写

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

使用倍角公式:

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

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

化简

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

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

分解

2 cos (x) + 4 cos (x) sin (x) : 2 cos (x) (2 sin (x) + 1)

2 cos (x) + 4 cos (x) sin (x)

将

4

改写为

2 \cdot 2

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

因式分解出通项

2 cos (x)

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

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

分别求解每个部分

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

2 sin (x) + 1 = 0 : x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

2 sin (x) + 1 = 0

将

1

到右边

2 sin (x) + 1 = 0

两边减去

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{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

合并所有解

x = \frac{π}{2} + 2 πn, x = \frac{3 π}{2} + 2 πn, x = \frac{7 π}{6} + 2 πn, x = \frac{11 π}{6} + 2 πn

作图

流行的例子

cosh (x) = \frac{3}{2}

(1+tan(t))/(sin(t))=0

\frac{1 + tan ( t )}{sin ( t )} = 0

sin^2(θ)+2cos(θ)= 7/4

sin^{2} (θ) + 2 cos (θ) = \frac{7}{4}

5cos(x)+3=3cos(x)+5

5 cos (x) + 3 = 3 cos (x) + 5

sin(pi/2)=cos(x)

sin (\frac{π}{2}) = cos (x)