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受欢迎的三角函数 >

2sec^2(θ)-3=tan^2(θ)

解答

2 sec^{2} (θ) - 3 = tan^{2} (θ)

解答

θ = \frac{π}{4} + 2 πn, θ = \frac{7 π}{4} + 2 πn, θ = \frac{3 π}{4} + 2 πn, θ = \frac{5 π}{4} + 2 πn

+1

度数

θ = 4 5^{\circ} + 36 0^{\circ} n, θ = 31 5^{\circ} + 36 0^{\circ} n, θ = 13 5^{\circ} + 36 0^{\circ} n, θ = 22 5^{\circ} + 36 0^{\circ} n

求解步骤

2 sec^{2} (θ) - 3 = tan^{2} (θ)

两边减去

tan^{2} (θ)

2 sec^{2} (θ) - 3 - tan^{2} (θ) = 0

使用三角恒等式改写

- 3 - tan^{2} (θ) + 2 sec^{2} (θ)

使用毕达哥拉斯恒等式:

tan^{2} (x) + 1 = sec^{2} (x)

tan^{2} (x) = sec^{2} (x) - 1

= - 3 - (sec^{2} (θ) - 1) + 2 sec^{2} (θ)

化简

- 3 - (sec^{2} (θ) - 1) + 2 sec^{2} (θ) : sec^{2} (θ) - 2

- 3 - (sec^{2} (θ) - 1) + 2 sec^{2} (θ)

- (sec^{2} (θ) - 1) : - sec^{2} (θ) + 1

- (sec^{2} (θ) - 1)

打开括号

= - (sec^{2} (θ)) - (- 1)

使用加减运算法则

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

= - sec^{2} (θ) + 1

= - 3 - sec^{2} (θ) + 1 + 2 sec^{2} (θ)

化简

- 3 - sec^{2} (θ) + 1 + 2 sec^{2} (θ) : sec^{2} (θ) - 2

- 3 - sec^{2} (θ) + 1 + 2 sec^{2} (θ)

对同类项分组

= - sec^{2} (θ) + 2 sec^{2} (θ) - 3 + 1

同类项相加:

- sec^{2} (θ) + 2 sec^{2} (θ) = sec^{2} (θ)

= sec^{2} (θ) - 3 + 1

数字相加/相减:

- 3 + 1 = - 2

= sec^{2} (θ) - 2

= sec^{2} (θ) - 2

= sec^{2} (θ) - 2

- 2 + sec^{2} (θ) = 0

用替代法求解

- 2 + sec^{2} (θ) = 0

令

: sec (θ) = u

- 2 + u^{2} = 0

- 2 + u^{2} = 0 : u = 2, u = - 2

- 2 + u^{2} = 0

将

2

到右边

- 2 + u^{2} = 0

两边加上

2

- 2 + u^{2} + 2 = 0 + 2

化简

u^{2} = 2

u^{2} = 2

对于

x^{2} = f (a)

解为

x = f (a), - f (a)

u = 2, u = - 2

u = sec (θ)

代回

sec (θ) = 2, sec (θ) = - 2

sec (θ) = 2, sec (θ) = - 2

sec (θ) = 2 : θ = \frac{π}{4} + 2 πn, θ = \frac{7 π}{4} + 2 πn

sec (θ) = 2

sec (θ) = 2

的通解

sec (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} sec (x) 1 \frac{2 3}{3} 22 Undefined - 2 - 2 - \frac{2 3}{3} 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} sec (x) - 1 - \frac{2 3}{3} - 2 - 2 Undefined 22 \frac{2 3}{3}

θ = \frac{π}{4} + 2 πn, θ = \frac{7 π}{4} + 2 πn

θ = \frac{π}{4} + 2 πn, θ = \frac{7 π}{4} + 2 πn

sec (θ) = - 2 : θ = \frac{3 π}{4} + 2 πn, θ = \frac{5 π}{4} + 2 πn

sec (θ) = - 2

sec (θ) = - 2

的通解

sec (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} sec (x) 1 \frac{2 3}{3} 22 Undefined - 2 - 2 - \frac{2 3}{3} 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} sec (x) - 1 - \frac{2 3}{3} - 2 - 2 Undefined 22 \frac{2 3}{3}

θ = \frac{3 π}{4} + 2 πn, θ = \frac{5 π}{4} + 2 πn

θ = \frac{3 π}{4} + 2 πn, θ = \frac{5 π}{4} + 2 πn

合并所有解

θ = \frac{π}{4} + 2 πn, θ = \frac{7 π}{4} + 2 πn, θ = \frac{3 π}{4} + 2 πn, θ = \frac{5 π}{4} + 2 πn

作图

流行的例子

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

sin (π - x) + cos (x) = 0

sin(x)=-sin(2x)

sin (x) = - sin (2 x)

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2cos(2θ)-3cos(θ)-2=0

2 cos (2 θ) - 3 cos (θ) - 2 = 0

tan(2θ)+6tan(θ)+8=0

tan (2 θ) + 6 tan (θ) + 8 = 0