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受欢迎的三角函数 >

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

解答

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

解答

x = 0.61547 \dots + 2 πn, x = π - 0.61547 \dots + 2 πn, x = - 0.61547 \dots + 2 πn, x = π + 0.61547 \dots + 2 πn

+1

度数

x = 35.26438 \dots^{\circ} + 36 0^{\circ} n, x = 144.73561 \dots^{\circ} + 36 0^{\circ} n, x = - 35.26438 \dots^{\circ} + 36 0^{\circ} n, x = 215.26438 \dots^{\circ} + 36 0^{\circ} n

求解步骤

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

两边减去

1 + sin^{2} (x)

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

使用三角恒等式改写

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

使用毕达哥拉斯恒等式:

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

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

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

化简

- 1 - sin^{2} (x) + 2 (1 - sin^{2} (x)) : - 3 sin^{2} (x) + 1

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

乘开

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

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

使用分配律:

a (b - c) = ab - a c

a = 2, b = 1, c = sin^{2} (x)

= 2 \cdot 1 - 2 sin^{2} (x)

数字相乘:

2 \cdot 1 = 2

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

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

化简

- 1 - sin^{2} (x) + 2 - 2 sin^{2} (x) : - 3 sin^{2} (x) + 1

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

对同类项分组

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

同类项相加:

- sin^{2} (x) - 2 sin^{2} (x) = - 3 sin^{2} (x)

= - 3 sin^{2} (x) - 1 + 2

数字相加/相减:

- 1 + 2 = 1

= - 3 sin^{2} (x) + 1

= - 3 sin^{2} (x) + 1

= - 3 sin^{2} (x) + 1

1 - 3 sin^{2} (x) = 0

用替代法求解

1 - 3 sin^{2} (x) = 0

令

: sin (x) = u

1 - 3 u^{2} = 0

1 - 3 u^{2} = 0 : u = \frac{1}{3}, u = - \frac{1}{3}

1 - 3 u^{2} = 0

将

1

到右边

1 - 3 u^{2} = 0

两边减去

1

1 - 3 u^{2} - 1 = 0 - 1

化简

- 3 u^{2} = - 1

- 3 u^{2} = - 1

两边除以

- 3

- 3 u^{2} = - 1

两边除以

- 3

\frac{- 3 u ^{2}}{- 3} = \frac{- 1}{- 3}

化简

u^{2} = \frac{1}{3}

u^{2} = \frac{1}{3}

对于

x^{2} = f (a)

解为

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

u = \frac{1}{3}, u = - \frac{1}{3}

u = sin (x)

代回

sin (x) = \frac{1}{3}, sin (x) = - \frac{1}{3}

sin (x) = \frac{1}{3}, sin (x) = - \frac{1}{3}

sin (x) = \frac{1}{3} : x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn

sin (x) = \frac{1}{3}

使用反三角函数性质

sin (x) = \frac{1}{3}

sin (x) = \frac{1}{3}

的通解

sin (x) = a \Rightarrow x = arcsin (a) + 2 πn, x = π - arcsin (a) + 2 πn

x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn

x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn

sin (x) = - \frac{1}{3} : x = arcsin (- \frac{1}{3}) + 2 πn, x = π + arcsin (\frac{1}{3}) + 2 πn

sin (x) = - \frac{1}{3}

使用反三角函数性质

sin (x) = - \frac{1}{3}

sin (x) = - \frac{1}{3}

的通解

sin (x) = - a \Rightarrow x = arcsin (- a) + 2 πn, x = π + arcsin (a) + 2 πn

x = arcsin (- \frac{1}{3}) + 2 πn, x = π + arcsin (\frac{1}{3}) + 2 πn

x = arcsin (- \frac{1}{3}) + 2 πn, x = π + arcsin (\frac{1}{3}) + 2 πn

合并所有解

x = arcsin (\frac{1}{3}) + 2 πn, x = π - arcsin (\frac{1}{3}) + 2 πn, x = arcsin (- \frac{1}{3}) + 2 πn, x = π + arcsin (\frac{1}{3}) + 2 πn

以小数形式表示解

x = 0.61547 \dots + 2 πn, x = π - 0.61547 \dots + 2 πn, x = - 0.61547 \dots + 2 πn, x = π + 0.61547 \dots + 2 πn

作图

流行的例子

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

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

- 1 + sin (x) = - 1

(sqrt(2))/2 =sin(θ)

\frac{2}{2} = sin (θ)

cos(a)=1,8b=1,5c=23

cos (a) = 1, 8 b = 1, 5 c = 23

sin(θ)cos(θ)=(2sqrt(3))/5

sin (θ) cos (θ) = \frac{2 3}{5}