解
−0.5cos(x)+0.8660200000000…sin(x)=−0.5
解
x=−2.09438…+2πn
+1
度
x=−119.99969…∘+360∘n解答ステップ
−0.5cos(x)+0.86602…sin(x)=−0.5
両辺に0.5cos(x)を足す0.86602…sin(x)=−0.5+0.5cos(x)
両辺を2乗する(0.86602…sin(x))2=(−0.5+0.5cos(x))2
両辺から(−0.5+0.5cos(x))2を引く0.7499906404sin2(x)−0.25+0.5cos(x)−0.25cos2(x)=0
三角関数の公式を使用して書き換える
−0.25−0.25cos2(x)+0.5cos(x)+0.7499906404sin2(x)
ピタゴラスの公式を使用する: cos2(x)+sin2(x)=1sin2(x)=1−cos2(x)=−0.25−0.25cos2(x)+0.5cos(x)+0.7499906404(1−cos2(x))
簡素化 −0.25−0.25cos2(x)+0.5cos(x)+0.7499906404(1−cos2(x)):0.5cos(x)−0.9999906404cos2(x)+0.4999906404
−0.25−0.25cos2(x)+0.5cos(x)+0.7499906404(1−cos2(x))
拡張 0.7499906404(1−cos2(x)):0.7499906404−0.74999…cos2(x)
0.74999…(1−cos2(x))
分配法則を適用する: a(b−c)=ab−aca=0.74999…,b=1,c=cos2(x)=0.74999…⋅1−0.74999…cos2(x)
=1⋅0.74999…−0.74999…cos2(x)
数を乗じる:1⋅0.74999…=0.74999…=0.74999…−0.74999…cos2(x)
=−0.25−0.25cos2(x)+0.5cos(x)+0.7499906404−0.74999…cos2(x)
簡素化 −0.25−0.25cos2(x)+0.5cos(x)+0.7499906404−0.74999…cos2(x):0.5cos(x)−0.9999906404cos2(x)+0.4999906404
−0.25−0.25cos2(x)+0.5cos(x)+0.7499906404−0.74999…cos2(x)
条件のようなグループ=−0.25cos2(x)+0.5cos(x)−0.7499906404cos2(x)−0.25+0.74999…
類似した元を足す:−0.25cos2(x)−0.7499906404cos2(x)=−0.9999906404cos2(x)=−0.9999906404cos2(x)+0.5cos(x)−0.25+0.74999…
数を足す/引く:−0.25+0.74999…=0.4999906404=0.5cos(x)−0.9999906404cos2(x)+0.4999906404
=0.5cos(x)−0.9999906404cos2(x)+0.4999906404
=0.5cos(x)−0.9999906404cos2(x)+0.4999906404
0.4999906404+0.5cos(x)−0.9999906404cos2(x)=0
置換で解く
0.4999906404+0.5cos(x)−0.9999906404cos2(x)=0
仮定:cos(x)=u0.4999906404+0.5u−0.9999906404u2=0
0.4999906404+0.5u−0.9999906404u2=0:u=−1.99998…−0.5+2.24994…,u=1.99998…0.5+2.24994…
0.4999906404+0.5u−0.9999906404u2=0
標準的な形式で書く ax2+bx+c=0−0.9999906404u2+0.5u+0.4999906404=0
解くとthe二次式
−0.9999906404u2+0.5u+0.4999906404=0
二次Equationの公式:
次の場合: a=−0.9999906404,b=0.5,c=0.4999906404u1,2=2(−0.9999906404)−0.5±0.52−4(−0.9999906404)⋅0.4999906404
u1,2=2(−0.9999906404)−0.5±0.52−4(−0.9999906404)⋅0.4999906404
0.52−4(−0.9999906404)⋅0.4999906404=2.24994…
0.52−4(−0.9999906404)⋅0.4999906404
規則を適用 −(−a)=a=0.52+4⋅0.9999906404⋅0.4999906404
数を乗じる:4⋅0.9999906404⋅0.4999906404=1.99994…=0.52+1.99994…
0.52=0.25=0.25+1.99994…
数を足す:0.25+1.99994…=2.24994…=2.24994…
u1,2=2(−0.9999906404)−0.5±2.24994…
解を分離するu1=2(−0.9999906404)−0.5+2.24994…,u2=2(−0.9999906404)−0.5−2.24994…
u=2(−0.9999906404)−0.5+2.24994…:−1.99998…−0.5+2.24994…
2(−0.9999906404)−0.5+2.24994…
括弧を削除する: (−a)=−a=−2⋅0.9999906404−0.5+2.24994…
数を乗じる:2⋅0.9999906404=1.99998…=−1.99998…−0.5+2.24994…
分数の規則を適用する: −ba=−ba=−1.99998…−0.5+2.24994…
u=2(−0.9999906404)−0.5−2.24994…:1.99998…0.5+2.24994…
2(−0.9999906404)−0.5−2.24994…
括弧を削除する: (−a)=−a=−2⋅0.9999906404−0.5−2.24994…
数を乗じる:2⋅0.9999906404=1.99998…=−1.99998…−0.5−2.24994…
分数の規則を適用する: −b−a=ba−0.5−2.24994…=−(0.5+2.24994…)=1.99998…0.5+2.24994…
二次equationの解:u=−1.99998…−0.5+2.24994…,u=1.99998…0.5+2.24994…
代用を戻す u=cos(x)cos(x)=−1.99998…−0.5+2.24994…,cos(x)=1.99998…0.5+2.24994…
cos(x)=−1.99998…−0.5+2.24994…,cos(x)=1.99998…0.5+2.24994…
cos(x)=−1.99998…−0.5+2.24994…:x=arccos(−1.99998…−0.5+2.24994…)+2πn,x=−arccos(−1.99998…−0.5+2.24994…)+2πn
cos(x)=−1.99998…−0.5+2.24994…
三角関数の逆数プロパティを適用する
cos(x)=−1.99998…−0.5+2.24994…
以下の一般解 cos(x)=−1.99998…−0.5+2.24994…cos(x)=−a⇒x=arccos(−a)+2πn,x=−arccos(−a)+2πnx=arccos(−1.99998…−0.5+2.24994…)+2πn,x=−arccos(−1.99998…−0.5+2.24994…)+2πn
x=arccos(−1.99998…−0.5+2.24994…)+2πn,x=−arccos(−1.99998…−0.5+2.24994…)+2πn
cos(x)=1.99998…0.5+2.24994…:解なし
cos(x)=1.99998…0.5+2.24994…
−1≤cos(x)≤1解なし
すべての解を組み合わせるx=arccos(−1.99998…−0.5+2.24994…)+2πn,x=−arccos(−1.99998…−0.5+2.24994…)+2πn
元のequationに当てはめて解を検算する
−0.5cos(x)+0.86602…sin(x)=−0.5 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(−1.99998…−0.5+2.24994…)+2πn:偽
arccos(−1.99998…−0.5+2.24994…)+2πn
挿入 n=1arccos(−1.99998…−0.5+2.24994…)+2π1
−0.5cos(x)+0.86602…sin(x)=−0.5の挿入向けx=arccos(−1.99998…−0.5+2.24994…)+2π1−0.5cos(arccos(−1.99998…−0.5+2.24994…)+2π1)+0.86602…sin(arccos(−1.99998…−0.5+2.24994…)+2π1)=−0.5
改良0.99999…=−0.5
⇒偽
解答を確認する −arccos(−1.99998…−0.5+2.24994…)+2πn:真
−arccos(−1.99998…−0.5+2.24994…)+2πn
挿入 n=1−arccos(−1.99998…−0.5+2.24994…)+2π1
−0.5cos(x)+0.86602…sin(x)=−0.5の挿入向けx=−arccos(−1.99998…−0.5+2.24994…)+2π1−0.5cos(−arccos(−1.99998…−0.5+2.24994…)+2π1)+0.86602…sin(−arccos(−1.99998…−0.5+2.24994…)+2π1)=−0.5
改良−0.5=−0.5
⇒真
x=−arccos(−1.99998…−0.5+2.24994…)+2πn
10進法形式で解を証明するx=−2.09438…+2πn