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129.8sin(a)-0.6129.8cos(a)=121.79

解答

12 \cdot 9.8 \cdot sin (a) - 0.6 \cdot 12 \cdot 9.8 \cdot cos (a) = 12 \cdot 1.79

解答

a = - 2.75844 \dots + 2 πn, a = 0.69769 \dots + 2 πn

+1

度数

a = - 158.04722 \dots^{\circ} + 36 0^{\circ} n, a = 39.97473 \dots^{\circ} + 36 0^{\circ} n

求解步骤

12 \cdot 9.8 sin (a) - 0.6 \cdot 12 \cdot 9.8 cos (a) = 12 \cdot 1.79

两边加上

0.6129.8 cos (a)

117.6 sin (a) = 21.48 + 70.56 cos (a)

两边进行平方

(117.6 sin (a))^{2} = (21.48 + 70.56 cos (a))^{2}

两边减去

(21.48 + 70.56 cos (a))^{2}

13829.76 sin^{2} (a) - 461.3904 - 3031.2576 cos (a) - 4978.7136 cos^{2} (a) = 0

使用三角恒等式改写

- 461.3904 + 13829.76 sin^{2} (a) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a)

使用毕达哥拉斯恒等式:

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

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

= - 461.3904 + 13829.76 (1 - cos^{2} (a)) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a)

化简

- 461.3904 + 13829.76 (1 - cos^{2} (a)) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a) : - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) + 13368.3696

- 461.3904 + 13829.76 (1 - cos^{2} (a)) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a)

乘开

13829.76 (1 - cos^{2} (a)) : 13829.76 - 13829.76 cos^{2} (a)

13829.76 (1 - cos^{2} (a))

使用分配律:

a (b - c) = ab - a c

a = 13829.76, b = 1, c = cos^{2} (a)

= 13829.76 \cdot 1 - 13829.76 cos^{2} (a)

= 1 \cdot 13829.76 - 13829.76 cos^{2} (a)

数字相乘:

1 \cdot 13829.76 = 13829.76

= 13829.76 - 13829.76 cos^{2} (a)

= - 461.3904 + 13829.76 - 13829.76 cos^{2} (a) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a)

化简

- 461.3904 + 13829.76 - 13829.76 cos^{2} (a) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a) : - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) + 13368.3696

- 461.3904 + 13829.76 - 13829.76 cos^{2} (a) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a)

对同类项分组

= - 13829.76 cos^{2} (a) - 3031.2576 cos (a) - 4978.7136 cos^{2} (a) - 461.3904 + 13829.76

同类项相加:

- 13829.76 cos^{2} (a) - 4978.7136 cos^{2} (a) = - 18808.4736 cos^{2} (a)

= - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) - 461.3904 + 13829.76

数字相加/相减:

- 461.3904 + 13829.76 = 13368.3696

= - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) + 13368.3696

= - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) + 13368.3696

= - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) + 13368.3696

13368.3696 - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) = 0

用替代法求解

13368.3696 - 18808.4736 cos^{2} (a) - 3031.2576 cos (a) = 0

令

: cos (a) = u

13368.3696 - 18808.4736 u^{2} - 3031.2576 u = 0

13368.3696 - 18808.4736 u^{2} - 3031.2576 u = 0 : u = - \frac{3031.2576 + 1014943029.424128}{37616.9472}, u = \frac{1014943029.424128 - 3031.2576}{37616.9472}

13368.3696 - 18808.4736 u^{2} - 3031.2576 u = 0

改写成标准形式

a x^{2} + b x + c = 0

- 18808.4736 u^{2} - 3031.2576 u + 13368.3696 = 0

使用求根公式求解

- 18808.4736 u^{2} - 3031.2576 u + 13368.3696 = 0

二次方程求根公式:

若

a = - 18808.4736, b = - 3031.2576, c = 13368.3696

u_{1, 2} = \frac{- ( - 3031.2576 ) \pm ( - 3031.2576 ) ^{2} - 4 ( - 18808.4736 ) \cdot 13368.3696}{2 ( - 18808.4736 )}

u_{1, 2} = \frac{- ( - 3031.2576 ) \pm ( - 3031.2576 ) ^{2} - 4 ( - 18808.4736 ) \cdot 13368.3696}{2 ( - 18808.4736 )}

(- 3031.2576)^{2} - 4 (- 18808.4736) \cdot 13368.3696 = 1014943029.424128

(- 3031.2576)^{2} - 4 (- 18808.4736) \cdot 13368.3696

使用法则

- (- a) = a

= (- 3031.2576)^{2} + 4 \cdot 18808.4736 \cdot 13368.3696

使用指数法则:

(- a)^{n} = a^{n},

若

n

是偶数

(- 3031.2576)^{2} = 3031.257 6^{2}

= 3031.257 6^{2} + 4 \cdot 13368.3696 \cdot 18808.4736

数字相乘:

4 \cdot 18808.4736 \cdot 13368.3696 = 1005754506.78657 \dots

= 3031.257 6^{2} + 1005754506.78657 \dots

3031.257 6^{2} = 9188522.63755 \dots

= 9188522.63755 \dots + 1005754506.78657 \dots

数字相加:

9188522.63755 \dots + 1005754506.78657 \dots = 1014943029.424128

= 1014943029.424128

u_{1, 2} = \frac{- ( - 3031.2576 ) \pm 1014943029.424128}{2 ( - 18808.4736 )}

将解分隔开

u_{1} = \frac{- ( - 3031.2576 ) + 1014943029.424128}{2 ( - 18808.4736 )}, u_{2} = \frac{- ( - 3031.2576 ) - 1014943029.424128}{2 ( - 18808.4736 )}

u = \frac{- ( - 3031.2576 ) + 1014943029.424128}{2 ( - 18808.4736 )} : - \frac{3031.2576 + 1014943029.424128}{37616.9472}

\frac{- ( - 3031.2576 ) + 1014943029.424128}{2 ( - 18808.4736 )}

去除括号:

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

= \frac{3031.2576 + 1014943029.424128}{- 2 \cdot 18808.4736}

数字相乘:

2 \cdot 18808.4736 = 37616.9472

= \frac{3031.2576 + 1014943029.424128}{- 37616.9472}

使用分式法则:

\frac{a}{- b} = - \frac{a}{b}

= - \frac{3031.2576 + 1014943029.424128}{37616.9472}

u = \frac{- ( - 3031.2576 ) - 1014943029.424128}{2 ( - 18808.4736 )} : \frac{1014943029.424128 - 3031.2576}{37616.9472}

\frac{- ( - 3031.2576 ) - 1014943029.424128}{2 ( - 18808.4736 )}

去除括号:

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

= \frac{3031.2576 - 1014943029.424128}{- 2 \cdot 18808.4736}

数字相乘:

2 \cdot 18808.4736 = 37616.9472

= \frac{3031.2576 - 1014943029.424128}{- 37616.9472}

使用分式法则:

\frac{- a}{- b} = \frac{a}{b}

3031.2576 - 1014943029.424128 = - (1014943029.424128 - 3031.2576)

= \frac{1014943029.424128 - 3031.2576}{37616.9472}

二次方程组的解是:

u = - \frac{3031.2576 + 1014943029.424128}{37616.9472}, u = \frac{1014943029.424128 - 3031.2576}{37616.9472}

u = cos (a)

代回

cos (a) = - \frac{3031.2576 + 1014943029.424128}{37616.9472}, cos (a) = \frac{1014943029.424128 - 3031.2576}{37616.9472}

cos (a) = - \frac{3031.2576 + 1014943029.424128}{37616.9472}, cos (a) = \frac{1014943029.424128 - 3031.2576}{37616.9472}

cos (a) = - \frac{3031.2576 + 1014943029.424128}{37616.9472} : a = arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn, a = - arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

cos (a) = - \frac{3031.2576 + 1014943029.424128}{37616.9472}

使用反三角函数性质

cos (a) = - \frac{3031.2576 + 1014943029.424128}{37616.9472}

cos (a) = - \frac{3031.2576 + 1014943029.424128}{37616.9472}

的通解

cos (x) = - a \Rightarrow x = arccos (- a) + 2 πn, x = - arccos (- a) + 2 πn

a = arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn, a = - arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

a = arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn, a = - arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

cos (a) = \frac{1014943029.424128 - 3031.2576}{37616.9472} : a = arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn, a = 2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

cos (a) = \frac{1014943029.424128 - 3031.2576}{37616.9472}

使用反三角函数性质

cos (a) = \frac{1014943029.424128 - 3031.2576}{37616.9472}

cos (a) = \frac{1014943029.424128 - 3031.2576}{37616.9472}

的通解

cos (x) = a \Rightarrow x = arccos (a) + 2 πn, x = 2 π - arccos (a) + 2 πn

a = arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn, a = 2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

a = arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn, a = 2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

合并所有解

a = arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn, a = - arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn, a = arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn, a = 2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

将解代入原方程进行验证

将它们代入

129.8 sin (a) - 0.6129.8 cos (a) = 121.79

检验解是否符合

去除与方程不符的解。

检验

arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

的解:

假

arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

代入

n = 1

arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1

对于

129.8 sin (a) - 0.6129.8 cos (a) = 121.79

代入

a = arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1

12 \cdot 9.8 sin (arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1) - 0.6 \cdot 12 \cdot 9.8 cos (arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1) = 12 \cdot 1.79

整理后得

109.40771 \dots = 21.48

\Rightarrow 假

检验

- arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

的解:

真

- arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn

代入

n = 1

- arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1

对于

129.8 sin (a) - 0.6129.8 cos (a) = 121.79

代入

a = - arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1

12 \cdot 9.8 sin (- arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1) - 0.6 \cdot 12 \cdot 9.8 cos (- arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 π 1) = 12 \cdot 1.79

整理后得

21.48 = 21.48

\Rightarrow 真

检验

arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

的解:

真

arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

代入

n = 1

arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1

对于

129.8 sin (a) - 0.6129.8 cos (a) = 121.79

代入

a = arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1

12 \cdot 9.8 sin (arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1) - 0.6 \cdot 12 \cdot 9.8 cos (arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1) = 12 \cdot 1.79

整理后得

21.48 = 21.48

\Rightarrow 真

检验

2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

的解:

假

2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

代入

n = 1

2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1

对于

129.8 sin (a) - 0.6129.8 cos (a) = 121.79

代入

a = 2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1

12 \cdot 9.8 sin (2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1) - 0.6 \cdot 12 \cdot 9.8 cos (2 π - arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 π 1) = 12 \cdot 1.79

整理后得

- 129.62418 \dots = 21.48

\Rightarrow 假

a = - arccos (- \frac{3031.2576 + 1014943029.424128}{37616.9472}) + 2 πn, a = arccos (\frac{1014943029.424128 - 3031.2576}{37616.9472}) + 2 πn

以小数形式表示解

a = - 2.75844 \dots + 2 πn, a = 0.69769 \dots + 2 πn

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