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受欢迎的三角函数 >

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

解答

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

解答

x = πn

+1

度数

x = 0^{\circ} + 18 0^{\circ} n

求解步骤

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

使用三角恒等式改写

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

使用毕达哥拉斯恒等式:

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

= 1

1 = cos (2 x)

交换两边

cos (2 x) = 1

cos (2 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}

2 x = 0 + 2 πn

2 x = 0 + 2 πn

解

2 x = 0 + 2 πn : x = πn

2 x = 0 + 2 πn

0 + 2 πn = 2 πn

2 x = 2 πn

两边除以

2

2 x = 2 πn

两边除以

2

\frac{2 x}{2} = \frac{2 πn}{2}

化简

x = πn

x = πn

x = πn

作图

流行的例子

(218)sin^2(x)+(126)sin(x)-88=0

(218) sin^{2} (x) + (126) sin (x) - 88 = 0

3 sin (3 x) = 0

cos(θ)csc(θ)=sin(θ)sec(θ)

cos (θ) csc (θ) = sin (θ) sec (θ)

64cos^2(θ)=49,(0<= ,θ<= 360)

64 cos^{2} (θ) = 49, (0^{\circ} \leq, θ \leq 36 0^{\circ})

solvefor y,x=4sec(y)

so l v e f or y, x = 4 sec (y)