解
sin(x)−0.5⋅cos(x)=0.768
解
x=2.84799…+2πn,x=1.22089…+2πn
+1
度
x=163.17825…∘+360∘n,x=69.95184…∘+360∘n解答ステップ
sin(x)−0.5cos(x)=0.768
両辺に0.5cos(x)を足すsin(x)=0.768+0.5cos(x)
両辺を2乗するsin2(x)=(0.768+0.5cos(x))2
両辺から(0.768+0.5cos(x))2を引くsin2(x)−0.589824−0.768cos(x)−0.25cos2(x)=0
三角関数の公式を使用して書き換える
−0.589824+sin2(x)−0.25cos2(x)−0.768cos(x)
ピタゴラスの公式を使用する: cos2(x)+sin2(x)=1sin2(x)=1−cos2(x)=−0.589824+1−cos2(x)−0.25cos2(x)−0.768cos(x)
簡素化 −0.589824+1−cos2(x)−0.25cos2(x)−0.768cos(x):−1.25cos2(x)−0.768cos(x)+0.410176
−0.589824+1−cos2(x)−0.25cos2(x)−0.768cos(x)
類似した元を足す:−cos2(x)−0.25cos2(x)=−1.25cos2(x)=−0.589824+1−1.25cos2(x)−0.768cos(x)
数を足す/引く:−0.589824+1=0.410176=−1.25cos2(x)−0.768cos(x)+0.410176
=−1.25cos2(x)−0.768cos(x)+0.410176
0.410176−0.768cos(x)−1.25cos2(x)=0
置換で解く
0.410176−0.768cos(x)−1.25cos2(x)=0
仮定:cos(x)=u0.410176−0.768u−1.25u2=0
0.410176−0.768u−1.25u2=0:u=−2.50.768+2.640704,u=2.52.640704−0.768
0.410176−0.768u−1.25u2=0
標準的な形式で書く ax2+bx+c=0−1.25u2−0.768u+0.410176=0
解くとthe二次式
−1.25u2−0.768u+0.410176=0
二次Equationの公式:
次の場合: a=−1.25,b=−0.768,c=0.410176u1,2=2(−1.25)−(−0.768)±(−0.768)2−4(−1.25)⋅0.410176
u1,2=2(−1.25)−(−0.768)±(−0.768)2−4(−1.25)⋅0.410176
(−0.768)2−4(−1.25)⋅0.410176=2.640704
(−0.768)2−4(−1.25)⋅0.410176
規則を適用 −(−a)=a=(−0.768)2+4⋅1.25⋅0.410176
指数の規則を適用する: n が偶数であれば (−a)n=an(−0.768)2=0.7682=0.7682+4⋅0.410176⋅1.25
数を乗じる:4⋅1.25⋅0.410176=2.05088=0.7682+2.05088
0.7682=0.589824=0.589824+2.05088
数を足す:0.589824+2.05088=2.640704=2.640704
u1,2=2(−1.25)−(−0.768)±2.640704
解を分離するu1=2(−1.25)−(−0.768)+2.640704,u2=2(−1.25)−(−0.768)−2.640704
u=2(−1.25)−(−0.768)+2.640704:−2.50.768+2.640704
2(−1.25)−(−0.768)+2.640704
括弧を削除する: (−a)=−a,−(−a)=a=−2⋅1.250.768+2.640704
数を乗じる:2⋅1.25=2.5=−2.50.768+2.640704
分数の規則を適用する: −ba=−ba=−2.50.768+2.640704
u=2(−1.25)−(−0.768)−2.640704:2.52.640704−0.768
2(−1.25)−(−0.768)−2.640704
括弧を削除する: (−a)=−a,−(−a)=a=−2⋅1.250.768−2.640704
数を乗じる:2⋅1.25=2.5=−2.50.768−2.640704
分数の規則を適用する: −b−a=ba0.768−2.640704=−(2.640704−0.768)=2.52.640704−0.768
二次equationの解:u=−2.50.768+2.640704,u=2.52.640704−0.768
代用を戻す u=cos(x)cos(x)=−2.50.768+2.640704,cos(x)=2.52.640704−0.768
cos(x)=−2.50.768+2.640704,cos(x)=2.52.640704−0.768
cos(x)=−2.50.768+2.640704:x=arccos(−2.50.768+2.640704)+2πn,x=−arccos(−2.50.768+2.640704)+2πn
cos(x)=−2.50.768+2.640704
三角関数の逆数プロパティを適用する
cos(x)=−2.50.768+2.640704
以下の一般解 cos(x)=−2.50.768+2.640704cos(x)=−a⇒x=arccos(−a)+2πn,x=−arccos(−a)+2πnx=arccos(−2.50.768+2.640704)+2πn,x=−arccos(−2.50.768+2.640704)+2πn
x=arccos(−2.50.768+2.640704)+2πn,x=−arccos(−2.50.768+2.640704)+2πn
cos(x)=2.52.640704−0.768:x=arccos(2.52.640704−0.768)+2πn,x=2π−arccos(2.52.640704−0.768)+2πn
cos(x)=2.52.640704−0.768
三角関数の逆数プロパティを適用する
cos(x)=2.52.640704−0.768
以下の一般解 cos(x)=2.52.640704−0.768cos(x)=a⇒x=arccos(a)+2πn,x=2π−arccos(a)+2πnx=arccos(2.52.640704−0.768)+2πn,x=2π−arccos(2.52.640704−0.768)+2πn
x=arccos(2.52.640704−0.768)+2πn,x=2π−arccos(2.52.640704−0.768)+2πn
すべての解を組み合わせるx=arccos(−2.50.768+2.640704)+2πn,x=−arccos(−2.50.768+2.640704)+2πn,x=arccos(2.52.640704−0.768)+2πn,x=2π−arccos(2.52.640704−0.768)+2πn
元のequationに当てはめて解を検算する
sin(x)−0.5cos(x)=0.768 に当てはめて解を確認する
equationに一致しないものを削除する。
解答を確認する arccos(−2.50.768+2.640704)+2πn:真
arccos(−2.50.768+2.640704)+2πn
挿入 n=1arccos(−2.50.768+2.640704)+2π1
sin(x)−0.5cos(x)=0.768の挿入向けx=arccos(−2.50.768+2.640704)+2π1sin(arccos(−2.50.768+2.640704)+2π1)−0.5cos(arccos(−2.50.768+2.640704)+2π1)=0.768
改良0.768=0.768
⇒真
解答を確認する −arccos(−2.50.768+2.640704)+2πn:偽
−arccos(−2.50.768+2.640704)+2πn
挿入 n=1−arccos(−2.50.768+2.640704)+2π1
sin(x)−0.5cos(x)=0.768の挿入向けx=−arccos(−2.50.768+2.640704)+2π1sin(−arccos(−2.50.768+2.640704)+2π1)−0.5cos(−arccos(−2.50.768+2.640704)+2π1)=0.768
改良0.18920…=0.768
⇒偽
解答を確認する arccos(2.52.640704−0.768)+2πn:真
arccos(2.52.640704−0.768)+2πn
挿入 n=1arccos(2.52.640704−0.768)+2π1
sin(x)−0.5cos(x)=0.768の挿入向けx=arccos(2.52.640704−0.768)+2π1sin(arccos(2.52.640704−0.768)+2π1)−0.5cos(arccos(2.52.640704−0.768)+2π1)=0.768
改良0.768=0.768
⇒真
解答を確認する 2π−arccos(2.52.640704−0.768)+2πn:偽
2π−arccos(2.52.640704−0.768)+2πn
挿入 n=12π−arccos(2.52.640704−0.768)+2π1
sin(x)−0.5cos(x)=0.768の挿入向けx=2π−arccos(2.52.640704−0.768)+2π1sin(2π−arccos(2.52.640704−0.768)+2π1)−0.5cos(2π−arccos(2.52.640704−0.768)+2π1)=0.768
改良−1.11080…=0.768
⇒偽
x=arccos(−2.50.768+2.640704)+2πn,x=arccos(2.52.640704−0.768)+2πn
10進法形式で解を証明するx=2.84799…+2πn,x=1.22089…+2πn