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人気のある三角関数 >

3+4cos(2x)+2cos(4x)=0

解

3 + 4 cos (2 x) + 2 cos (4 x) = 0

解

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

+1

度

x = 6 0^{\circ} + 18 0^{\circ} n, x = 12 0^{\circ} + 18 0^{\circ} n

解答ステップ

3 + 4 cos (2 x) + 2 cos (4 x) = 0

三角関数の公式を使用して書き換える

3 + 2 cos (4 x) + 4 cos (2 x)

cos (4 x) = 2 cos^{2} (2 x) - 1

cos (4 x)

書き換え

= cos (2 \cdot 2 x)

2倍角の公式を使用:

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

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

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

= 3 + 2 (2 cos^{2} (2 x) - 1) + 4 cos (2 x)

簡素化

3 + 2 (2 cos^{2} (2 x) - 1) + 4 cos (2 x) : 4 cos^{2} (2 x) + 4 cos (2 x) + 1

3 + 2 (2 cos^{2} (2 x) - 1) + 4 cos (2 x)

拡張

2 (2 cos^{2} (2 x) - 1) : 4 cos^{2} (2 x) - 2

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

分配法則を適用する:

a (b - c) = ab - a c

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

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

簡素化

2 \cdot 2 cos^{2} (2 x) - 2 \cdot 1 : 4 cos^{2} (2 x) - 2

2 \cdot 2 cos^{2} (2 x) - 2 \cdot 1

数を乗じる:

2 \cdot 2 = 4

= 4 cos^{2} (2 x) - 2 \cdot 1

数を乗じる:

2 \cdot 1 = 2

= 4 cos^{2} (2 x) - 2

= 4 cos^{2} (2 x) - 2

= 3 + 4 cos^{2} (2 x) - 2 + 4 cos (2 x)

簡素化

3 + 4 cos^{2} (2 x) - 2 + 4 cos (2 x) : 4 cos^{2} (2 x) + 4 cos (2 x) + 1

3 + 4 cos^{2} (2 x) - 2 + 4 cos (2 x)

条件のようなグループ

= 4 cos^{2} (2 x) + 4 cos (2 x) + 3 - 2

数を足す/引く:

3 - 2 = 1

= 4 cos^{2} (2 x) + 4 cos (2 x) + 1

= 4 cos^{2} (2 x) + 4 cos (2 x) + 1

= 4 cos^{2} (2 x) + 4 cos (2 x) + 1

1 + 4 cos (2 x) + 4 cos^{2} (2 x) = 0

置換で解く

1 + 4 cos (2 x) + 4 cos^{2} (2 x) = 0

仮定:

cos (2 x) = u

1 + 4 u + 4 u^{2} = 0

1 + 4 u + 4 u^{2} = 0 : u = - \frac{1}{2}

1 + 4 u + 4 u^{2} = 0

標準的な形式で書く

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

4 u^{2} + 4 u + 1 = 0

解くとthe二次式

4 u^{2} + 4 u + 1 = 0

二次Equationの公式:

次の場合:

a = 4, b = 4, c = 1

u_{1, 2} = \frac{- 4 \pm 4 ^{2} - 4 \cdot 4 \cdot 1}{2 \cdot 4}

u_{1, 2} = \frac{- 4 \pm 4 ^{2} - 4 \cdot 4 \cdot 1}{2 \cdot 4}

4^{2} - 4 \cdot 4 \cdot 1 = 0

4^{2} - 4 \cdot 4 \cdot 1

数を乗じる:

4 \cdot 4 \cdot 1 = 16

= 4^{2} - 16

4^{2} = 16

= 16 - 16

数を引く:

16 - 16 = 0

= 0

u_{1, 2} = \frac{- 4 \pm 0}{2 \cdot 4}

u = \frac{- 4}{2 \cdot 4}

\frac{- 4}{2 \cdot 4} = - \frac{1}{2}

\frac{- 4}{2 \cdot 4}

数を乗じる:

2 \cdot 4 = 8

= \frac{- 4}{8}

分数の規則を適用する:

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

= - \frac{4}{8}

共通因数を約分する:

4

= - \frac{1}{2}

u = - \frac{1}{2}

二次equationの解:

u = - \frac{1}{2}

代用を戻す

u = cos (2 x)

cos (2 x) = - \frac{1}{2}

cos (2 x) = - \frac{1}{2}

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

cos (2 x) = - \frac{1}{2}

以下の一般解

cos (2 x) = - \frac{1}{2}

cos (x)

2 πn

循環を含む周期性テーブル:

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

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

解く

2 x = \frac{2 π}{3} + 2 πn : x = \frac{π}{3} + πn

2 x = \frac{2 π}{3} + 2 πn

以下で両辺を割る

2

2 x = \frac{2 π}{3} + 2 πn

以下で両辺を割る

2

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

簡素化

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

簡素化

\frac{2 x}{2} : x

\frac{2 x}{2}

数を割る:

\frac{2}{2} = 1

= x

簡素化

\frac{\frac{2 π}{3}}{2} + \frac{2 πn}{2} : \frac{π}{3} + πn

\frac{\frac{2 π}{3}}{2} + \frac{2 πn}{2}

\frac{\frac{2 π}{3}}{2} = \frac{π}{3}

\frac{\frac{2 π}{3}}{2}

分数の規則を適用する:

\frac{\frac{b}{c}}{a} = \frac{b}{c \cdot a}

= \frac{2 π}{3 \cdot 2}

数を乗じる:

3 \cdot 2 = 6

= \frac{2 π}{6}

共通因数を約分する:

2

= \frac{π}{3}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

数を割る:

\frac{2}{2} = 1

= πn

= \frac{π}{3} + πn

x = \frac{π}{3} + πn

x = \frac{π}{3} + πn

x = \frac{π}{3} + πn

解く

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

2 x = \frac{4 π}{3} + 2 πn

以下で両辺を割る

2

2 x = \frac{4 π}{3} + 2 πn

以下で両辺を割る

2

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

簡素化

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

簡素化

\frac{2 x}{2} : x

\frac{2 x}{2}

数を割る:

\frac{2}{2} = 1

= x

簡素化

\frac{\frac{4 π}{3}}{2} + \frac{2 πn}{2} : \frac{2 π}{3} + πn

\frac{\frac{4 π}{3}}{2} + \frac{2 πn}{2}

\frac{\frac{4 π}{3}}{2} = \frac{2 π}{3}

\frac{\frac{4 π}{3}}{2}

分数の規則を適用する:

\frac{\frac{b}{c}}{a} = \frac{b}{c \cdot a}

= \frac{4 π}{3 \cdot 2}

数を乗じる:

3 \cdot 2 = 6

= \frac{4 π}{6}

共通因数を約分する:

2

= \frac{2 π}{3}

\frac{2 πn}{2} = πn

\frac{2 πn}{2}

数を割る:

\frac{2}{2} = 1

= πn

= \frac{2 π}{3} + πn

x = \frac{2 π}{3} + πn

x = \frac{2 π}{3} + πn

x = \frac{2 π}{3} + πn

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

すべての解を組み合わせる

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

グラフ

人気の例

cos(θ)=-4/5 ,sin(2θ),180<θ<270

cos (θ) = - \frac{4}{5}, sin (2 θ), 18 0^{\circ} < θ < 27 0^{\circ}

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

4cos^2(x)=5-4sin(x),0<= x<= 2pi

4 cos^{2} (x) = 5 - 4 sin (x), 0 \leq x \leq 2 π

0 = 6 sin (x)

tan^2(x)+1=4tan(x)

tan^{2} (x) + 1 = 4 tan (x)