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受欢迎的三角函数 >

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

解答

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

解答

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

+1

度数

x = 0^{\circ} + 36 0^{\circ} n, x = 18 0^{\circ} + 36 0^{\circ} n, x = 13 5^{\circ} + 18 0^{\circ} n

求解步骤

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

使用三角恒等式改写

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

使用倍角公式:

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

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

使用倍角公式:

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

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

化简

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

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

分解

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

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

使用指数法则:

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

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

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

因式分解出通项

- 2 sin (x)

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

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

分别求解每个部分

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

sin (x) + cos (x) = 0 : x = \frac{3 π}{4} + πn

sin (x) + cos (x) = 0

使用三角恒等式改写

sin (x) + cos (x) = 0

在两边除以

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

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

化简

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

使用基本三角恒等式:

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

tan (x) + 1 = 0

tan (x) + 1 = 0

将

1

到右边

tan (x) + 1 = 0

两边减去

1

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

化简

tan (x) = - 1

tan (x) = - 1

tan (x) = - 1

的通解

tan (x)

周期表（周期为

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} tan (x) 0 \frac{3}{3} 13 \pm \infty - 3 - 1 - \frac{3}{3}

x = \frac{3 π}{4} + πn

x = \frac{3 π}{4} + πn

合并所有解

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

作图

流行的例子

-4cos^2(θ)=-6cos^2(θ)+1

- 4 cos^{2} (θ) = - 6 cos^{2} (θ) + 1

cos(4x)-3cos(2x)-1=0

cos (4 x) - 3 cos (2 x) - 1 = 0

7 sin (x) + 2 = 0

sin(x+30)=cos(x+60)

sin (x + 3 0^{\circ}) = cos (x + 6 0^{\circ})

cos(5x+40)= 3/5

cos (5 x + 4 0^{\circ}) = \frac{3}{5}