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人気のある三角関数 >

4cos^2(x)+cos(2x)-7cos(x)=-2,0<= x<= 360

解

4 cos^{2} (x) + cos (2 x) - 7 cos (x) = - 2, 0^{\circ} \leq x \leq 36 0^{\circ}

解

x = 0, x = 36 0^{\circ}, x = 1.40334 \dots, x = 36 0^{\circ} - 1.40334 \dots

+1

ラジアン

x = 0, x = 2 π, x = 1.40334 \dots, x = 2 π - 1.40334 \dots

解答ステップ

4 cos^{2} (x) + cos (2 x) - 7 cos (x) = - 2, 0^{\circ} \leq x \leq 36 0^{\circ}

両辺から

- 2

を引く

4 cos^{2} (x) + cos (2 x) - 7 cos (x) + 2 = 0

三角関数の公式を使用して書き換える

2 + cos (2 x) + 4 cos^{2} (x) - 7 cos (x)

2倍角の公式を使用:

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

= 2 + 2 cos^{2} (x) - 1 + 4 cos^{2} (x) - 7 cos (x)

簡素化

2 + 2 cos^{2} (x) - 1 + 4 cos^{2} (x) - 7 cos (x) : 6 cos^{2} (x) - 7 cos (x) + 1

2 + 2 cos^{2} (x) - 1 + 4 cos^{2} (x) - 7 cos (x)

条件のようなグループ

= 2 cos^{2} (x) + 4 cos^{2} (x) - 7 cos (x) + 2 - 1

類似した元を足す:

2 cos^{2} (x) + 4 cos^{2} (x) = 6 cos^{2} (x)

= 6 cos^{2} (x) - 7 cos (x) + 2 - 1

数を足す/引く:

2 - 1 = 1

= 6 cos^{2} (x) - 7 cos (x) + 1

= 6 cos^{2} (x) - 7 cos (x) + 1

1 + 6 cos^{2} (x) - 7 cos (x) = 0

置換で解く

1 + 6 cos^{2} (x) - 7 cos (x) = 0

仮定:

cos (x) = u

1 + 6 u^{2} - 7 u = 0

1 + 6 u^{2} - 7 u = 0 : u = 1, u = \frac{1}{6}

1 + 6 u^{2} - 7 u = 0

標準的な形式で書く

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

6 u^{2} - 7 u + 1 = 0

解くとthe二次式

6 u^{2} - 7 u + 1 = 0

二次Equationの公式:

次の場合:

a = 6, b = - 7, c = 1

u_{1, 2} = \frac{- ( - 7 ) \pm ( - 7 ) ^{2} - 4 \cdot 6 \cdot 1}{2 \cdot 6}

u_{1, 2} = \frac{- ( - 7 ) \pm ( - 7 ) ^{2} - 4 \cdot 6 \cdot 1}{2 \cdot 6}

(- 7)^{2} - 4 \cdot 6 \cdot 1 = 5

(- 7)^{2} - 4 \cdot 6 \cdot 1

指数の規則を適用する:

n

が偶数であれば

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

(- 7)^{2} = 7^{2}

= 7^{2} - 4 \cdot 6 \cdot 1

数を乗じる:

4 \cdot 6 \cdot 1 = 24

= 7^{2} - 24

7^{2} = 49

= 49 - 24

数を引く:

49 - 24 = 25

= 25

数を因数に分解する:

25 = 5^{2}

= 5^{2}

累乗根の規則を適用する:

n a^{n} = a

5^{2} = 5

= 5

u_{1, 2} = \frac{- ( - 7 ) \pm 5}{2 \cdot 6}

解を分離する

u_{1} = \frac{- ( - 7 ) + 5}{2 \cdot 6}, u_{2} = \frac{- ( - 7 ) - 5}{2 \cdot 6}

u = \frac{- ( - 7 ) + 5}{2 \cdot 6} : 1

\frac{- ( - 7 ) + 5}{2 \cdot 6}

規則を適用

- (- a) = a

= \frac{7 + 5}{2 \cdot 6}

数を足す:

7 + 5 = 12

= \frac{12}{2 \cdot 6}

数を乗じる:

2 \cdot 6 = 12

= \frac{12}{12}

規則を適用

\frac{a}{a} = 1

= 1

u = \frac{- ( - 7 ) - 5}{2 \cdot 6} : \frac{1}{6}

\frac{- ( - 7 ) - 5}{2 \cdot 6}

規則を適用

- (- a) = a

= \frac{7 - 5}{2 \cdot 6}

数を引く:

7 - 5 = 2

= \frac{2}{2 \cdot 6}

数を乗じる:

2 \cdot 6 = 12

= \frac{2}{12}

共通因数を約分する:

2

= \frac{1}{6}

二次equationの解:

u = 1, u = \frac{1}{6}

代用を戻す

u = cos (x)

cos (x) = 1, cos (x) = \frac{1}{6}

cos (x) = 1, cos (x) = \frac{1}{6}

cos (x) = 1, 0 \leq x \leq 36 0^{\circ} : x = 0, x = 36 0^{\circ}

cos (x) = 1, 0 \leq x \leq 36 0^{\circ}

以下の一般解

cos (x) = 1

cos (x)

36 0^{\circ} n

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}

x = 0 + 36 0^{\circ} n

x = 0 + 36 0^{\circ} n

解く

x = 0 + 36 0^{\circ} n : x = 36 0^{\circ} n

x = 0 + 36 0^{\circ} n

0 + 36 0^{\circ} n = 36 0^{\circ} n

x = 36 0^{\circ} n

x = 36 0^{\circ} n

範囲の解答

0 \leq x \leq 36 0^{\circ}

x = 0, x = 36 0^{\circ}

cos (x) = \frac{1}{6}, 0 \leq x \leq 36 0^{\circ} : x = arccos (\frac{1}{6}), x = 36 0^{\circ} - arccos (\frac{1}{6})

cos (x) = \frac{1}{6}, 0 \leq x \leq 36 0^{\circ}

三角関数の逆数プロパティを適用する

cos (x) = \frac{1}{6}

以下の一般解

cos (x) = \frac{1}{6}

cos (x) = a \Rightarrow x = arccos (a) + 36 0^{\circ} n, x = 36 0^{\circ} - arccos (a) + 36 0^{\circ} n

x = arccos (\frac{1}{6}) + 36 0^{\circ} n, x = 36 0^{\circ} - arccos (\frac{1}{6}) + 36 0^{\circ} n

x = arccos (\frac{1}{6}) + 36 0^{\circ} n, x = 36 0^{\circ} - arccos (\frac{1}{6}) + 36 0^{\circ} n

範囲の解答

0 \leq x \leq 36 0^{\circ}

x = arccos (\frac{1}{6}), x = 36 0^{\circ} - arccos (\frac{1}{6})

すべての解を組み合わせる

x = 0, x = 36 0^{\circ}, x = arccos (\frac{1}{6}), x = 36 0^{\circ} - arccos (\frac{1}{6})

10進法形式で解を証明する

x = 0, x = 36 0^{\circ}, x = 1.40334 \dots, x = 36 0^{\circ} - 1.40334 \dots

グラフ

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