해법
cos(3x)cos(x)=2cos(2x)cos(x)
해법
x=2π+2πn,x=23π+2πn,x=1.04719…+2πn,x=2π−1.04719…+2πn,x=2.46670…+2πn,x=−2.46670…+2πn
+1
도
x=90∘+360∘n,x=270∘+360∘n,x=60.00000…∘+360∘n,x=299.99999…∘+360∘n,x=141.33171…∘+360∘n,x=−141.33171…∘+360∘n솔루션 단계
cos(3x)cos(x)=2cos(2x)cos(x)
빼다 2cos(2x)cos(x) 양쪽에서cos(3x)cos(x)−2cos(2x)cos(x)=0
삼각성을 사용하여 다시 쓰기
cos(3x)cos(x)−2cos(2x)cos(x)
더블 앵글 아이덴티티 사용: cos(2x)=2cos2(x)−1=cos(3x)cos(x)−2(2cos2(x)−1)cos(x)
cos(3x)cos(x)−(−1+2cos2(x))⋅2cos(x)=0
cos(3x)cos(x)−(−1+2cos2(x))⋅2cos(x)요인:cos(x)(cos(3x)−2(2cos(x)+1)(2cos(x)−1))
cos(3x)cos(x)−(−1+2cos2(x))⋅2cos(x)
공통 용어를 추출하다 cos(x)=cos(x)(cos(3x)−2(−1+cos2(x)⋅2))
cos(3x)−2(2cos2(x)−1)요인:cos(3x)−2(2cos(x)+1)(2cos(x)−1)
cos(3x)−2(−1+cos2(x)⋅2)
−1+cos2(x)⋅2요인:(2cos(x)+1)(2cos(x)−1)
−1+cos2(x)⋅2
2cos2(x)−1(2cos(x))2−12 로 다시 씁니다
2cos2(x)−1
급진적인 규칙 적용: a=(a)22=(2)2=(2)2cos2(x)−1
112 로 다시 씁니다 =(2)2cos2(x)−12
지수 규칙 적용: ambm=(ab)m(2)2cos2(x)=(2cos(x))2=(2cos(x))2−12
=(2cos(x))2−12
두 제곱 공식의 차이 적용: x2−y2=(x+y)(x−y)(2cos(x))2−12=(2cos(x)+1)(2cos(x)−1)=(2cos(x)+1)(2cos(x)−1)
=cos(3x)−2(2cos(x)+1)(2cos(x)−1)
=cos(x)(cos(3x)−2(2cos(x)+1)(2cos(x)−1))
cos(x)(cos(3x)−2(2cos(x)+1)(2cos(x)−1))=0
각 부분을 개별적으로 해결cos(x)=0orcos(3x)−2(2cos(x)+1)(2cos(x)−1)=0
cos(x)=0:x=2π+2πn,x=23π+2πn
cos(x)=0
일반 솔루션 cos(x)=0
cos(x) 주기율표 2πn 주기:
x06π4π3π2π32π43π65πcos(x)12322210−21−22−23xπ67π45π34π23π35π47π611πcos(x)−1−23−22−210212223
x=2π+2πn,x=23π+2πn
x=2π+2πn,x=23π+2πn
cos(3x)−2(2cos(x)+1)(2cos(x)−1)=0:x=arccos(0.50000…)+2πn,x=2π−arccos(0.50000…)+2πn,x=arccos(−0.78077…)+2πn,x=−arccos(−0.78077…)+2πn
cos(3x)−2(2cos(x)+1)(2cos(x)−1)=0
삼각성을 사용하여 다시 쓰기
cos(3x)−(−1+cos(x)2)(1+cos(x)2)⋅2
cos(3x)=4cos3(x)−3cos(x)
cos(3x)
삼각성을 사용하여 다시 쓰기
cos(3x)
로 고쳐 쓰다=cos(2x+x)
앵글섬식별사용: cos(s+t)=cos(s)cos(t)−sin(s)sin(t)=cos(2x)cos(x)−sin(2x)sin(x)
더블 앵글 아이덴티티 사용: sin(2x)=2sin(x)cos(x)=cos(2x)cos(x)−2sin(x)cos(x)sin(x)
cos(2x)cos(x)−2sin(x)cos(x)sin(x)단순화하세요:cos(x)cos(2x)−2sin2(x)cos(x)
cos(2x)cos(x)−2sin(x)cos(x)sin(x)
2sin(x)cos(x)sin(x)=2sin2(x)cos(x)
2sin(x)cos(x)sin(x)
지수 규칙 적용: ab⋅ac=ab+csin(x)sin(x)=sin1+1(x)=2cos(x)sin1+1(x)
숫자 추가: 1+1=2=2cos(x)sin2(x)
=cos(x)cos(2x)−2sin2(x)cos(x)
=cos(x)cos(2x)−2sin2(x)cos(x)
=cos(x)cos(2x)−2sin2(x)cos(x)
더블 앵글 아이덴티티 사용: cos(2x)=2cos2(x)−1=(2cos2(x)−1)cos(x)−2sin2(x)cos(x)
피타고라스 정체성 사용: cos2(x)+sin2(x)=1sin2(x)=1−cos2(x)=(2cos2(x)−1)cos(x)−2(1−cos2(x))cos(x)
(2cos2(x)−1)cos(x)−2(1−cos2(x))cos(x)확대한다:4cos3(x)−3cos(x)
(2cos2(x)−1)cos(x)−2(1−cos2(x))cos(x)
=cos(x)(2cos2(x)−1)−2cos(x)(1−cos2(x))
cos(x)(2cos2(x)−1)확대한다:2cos3(x)−cos(x)
cos(x)(2cos2(x)−1)
분배 법칙 적용: a(b−c)=ab−aca=cos(x),b=2cos2(x),c=1=cos(x)2cos2(x)−cos(x)1
=2cos2(x)cos(x)−1cos(x)
2cos2(x)cos(x)−1⋅cos(x)단순화하세요:2cos3(x)−cos(x)
2cos2(x)cos(x)−1cos(x)
2cos2(x)cos(x)=2cos3(x)
2cos2(x)cos(x)
지수 규칙 적용: ab⋅ac=ab+ccos2(x)cos(x)=cos2+1(x)=2cos2+1(x)
숫자 추가: 2+1=3=2cos3(x)
1⋅cos(x)=cos(x)
1cos(x)
곱하다: 1⋅cos(x)=cos(x)=cos(x)
=2cos3(x)−cos(x)
=2cos3(x)−cos(x)
=2cos3(x)−cos(x)−2(1−cos2(x))cos(x)
−2cos(x)(1−cos2(x))확대한다:−2cos(x)+2cos3(x)
−2cos(x)(1−cos2(x))
분배 법칙 적용: a(b−c)=ab−aca=−2cos(x),b=1,c=cos2(x)=−2cos(x)1−(−2cos(x))cos2(x)
마이너스 플러스 규칙 적용−(−a)=a=−2⋅1cos(x)+2cos2(x)cos(x)
−2⋅1⋅cos(x)+2cos2(x)cos(x)단순화하세요:−2cos(x)+2cos3(x)
−2⋅1cos(x)+2cos2(x)cos(x)
2⋅1⋅cos(x)=2cos(x)
2⋅1cos(x)
숫자를 곱하시오: 2⋅1=2=2cos(x)
2cos2(x)cos(x)=2cos3(x)
2cos2(x)cos(x)
지수 규칙 적용: ab⋅ac=ab+ccos2(x)cos(x)=cos2+1(x)=2cos2+1(x)
숫자 추가: 2+1=3=2cos3(x)
=−2cos(x)+2cos3(x)
=−2cos(x)+2cos3(x)
=2cos3(x)−cos(x)−2cos(x)+2cos3(x)
2cos3(x)−cos(x)−2cos(x)+2cos3(x)단순화하세요:4cos3(x)−3cos(x)
2cos3(x)−cos(x)−2cos(x)+2cos3(x)
집단적 용어=2cos3(x)+2cos3(x)−cos(x)−2cos(x)
유사 요소 추가: 2cos3(x)+2cos3(x)=4cos3(x)=4cos3(x)−cos(x)−2cos(x)
유사 요소 추가: −cos(x)−2cos(x)=−3cos(x)=4cos3(x)−3cos(x)
=4cos3(x)−3cos(x)
=4cos3(x)−3cos(x)
=4cos3(x)−3cos(x)−2(−1+2cos(x))(1+2cos(x))
−3cos(x)+4cos3(x)−(−1+cos(x)2)(1+cos(x)2)⋅2=0
대체로 해결
−3cos(x)+4cos3(x)−(−1+cos(x)2)(1+cos(x)2)⋅2=0
하게: cos(x)=u−3u+4u3−(−1+u2)(1+u2)⋅2=0
−3u+4u3−(−1+u2)(1+u2)⋅2=0:u≈1.28077…,u≈0.50000…,u≈−0.78077…
−3u+4u3−(−1+u2)(1+u2)⋅2=0
−3u+4u3−(−1+u2)(1+u2)⋅2 확장 :−3u+4u3−4u2+2
−3u+4u3−(−1+u2)(1+u2)⋅2
=−3u+4u3−2(−1+2u)(1+2u)
−(−1+u2)(1+u2)⋅2확대한다:−4u2+2
(−1+u2)(1+u2)확대한다:2u2−1
(−1+u2)(1+u2)
두 제곱 공식의 차이 적용: (a−b)(a+b)=a2−b2a=u2,b=1=(u2)2−12
(u2)2−12단순화하세요:2u2−1
(u2)2−12
규칙 적용 1a=112=1=(2u)2−1
(u2)2=2u2
(u2)2
지수 규칙 적용: (a⋅b)n=anbn=(2)2u2
(2)2:2
급진적인 규칙 적용: a=a21=(221)2
지수 규칙 적용: (ab)c=abc=221⋅2
21⋅2=1
21⋅2
다중 분수: a⋅cb=ca⋅b=21⋅2
공통 요인 취소: 2=1
=2
=u2⋅2
=2u2−1
=2u2−1
=−2(2u2−1)
−2(2u2−1)확대한다:−4u2+2
−2(2u2−1)
분배 법칙 적용: a(b−c)=ab−aca=−2,b=2u2,c=1=−2⋅2u2−(−2)⋅1
마이너스 플러스 규칙 적용−(−a)=a=−2⋅2u2+2⋅1
−2⋅2u2+2⋅1단순화하세요:−4u2+2
−2⋅2u2+2⋅1
숫자를 곱하시오: 2⋅2=4=−4u2+2⋅1
숫자를 곱하시오: 2⋅1=2=−4u2+2
=−4u2+2
=−4u2+2
=−3u+4u3−4u2+2
−3u+4u3−4u2+2=0
표준 양식으로 작성 anxn+…+a1x+a0=04u3−4u2−3u+2=0
다음을 위한 하나의 솔루션 찾기 4u3−4u2−3u+2=0 뉴턴-랩슨을 이용하여:u≈1.28077…
4u3−4u2−3u+2=0
뉴턴-랩슨 근사 정의
f(u)=4u3−4u2−3u+2
f′(u)찾다 :12u2−8u−3
dud(4u3−4u2−3u+2)
합계/차이 규칙 적용: (f±g)′=f′±g′=dud(4u3)−dud(4u2)−dud(3u)+dud(2)
dud(4u3)=12u2
dud(4u3)
정수를 빼라: (a⋅f)′=a⋅f′=4dud(u3)
전원 규칙을 적용합니다: dxd(xa)=a⋅xa−1=4⋅3u3−1
단순화=12u2
dud(4u2)=8u
dud(4u2)
정수를 빼라: (a⋅f)′=a⋅f′=4dud(u2)
전원 규칙을 적용합니다: dxd(xa)=a⋅xa−1=4⋅2u2−1
단순화=8u
dud(3u)=3
dud(3u)
정수를 빼라: (a⋅f)′=a⋅f′=3dudu
공통 도함수 적용: dudu=1=3⋅1
단순화=3
dud(2)=0
dud(2)
상수의 도함수: dxd(a)=0=0
=12u2−8u−3+0
단순화=12u2−8u−3
렛 u0=1계산하다 un+1 까지 Δun+1<0.000001
u1=2:Δu1=1
f(u0)=4⋅13−4⋅12−3⋅1+2=−1f′(u0)=12⋅12−8⋅1−3=1u1=2
Δu1=∣2−1∣=1Δu1=1
u2=1.58620…:Δu2=0.41379…
f(u1)=4⋅23−4⋅22−3⋅2+2=12f′(u1)=12⋅22−8⋅2−3=29u2=1.58620…
Δu2=∣1.58620…−2∣=0.41379…Δu2=0.41379…
u3=1.36962…:Δu3=0.21658…
f(u2)=4⋅1.58620…3−4⋅1.58620…2−3⋅1.58620…+2=3.14108…f′(u2)=12⋅1.58620…2−8⋅1.58620…−3=14.50297…u3=1.36962…
Δu3=∣1.36962…−1.58620…∣=0.21658…Δu3=0.21658…
u4=1.29192…:Δu4=0.07769…
f(u3)=4⋅1.36962…3−4⋅1.36962…2−3⋅1.36962…+2=0.66459…f′(u3)=12⋅1.36962…2−8⋅1.36962…−3=8.55345…u4=1.29192…
Δu4=∣1.29192…−1.36962…∣=0.07769…Δu4=0.07769…
u5=1.28098…:Δu5=0.01093…
f(u4)=4⋅1.29192…3−4⋅1.29192…2−3⋅1.29192…+2=0.07319…f′(u4)=12⋅1.29192…2−8⋅1.29192…−3=6.69344…u5=1.28098…
Δu5=∣1.28098…−1.29192…∣=0.01093…Δu5=0.01093…
u6=1.28077…:Δu6=0.00021…
f(u5)=4⋅1.28098…3−4⋅1.28098…2−3⋅1.28098…+2=0.00137…f′(u5)=12⋅1.28098…2−8⋅1.28098…−3=6.44328…u6=1.28077…
Δu6=∣1.28077…−1.28098…∣=0.00021…Δu6=0.00021…
u7=1.28077…:Δu7=7.99005E−8
f(u6)=4⋅1.28077…3−4⋅1.28077…2−3⋅1.28077…+2=5.14435E−7f′(u6)=12⋅1.28077…2−8⋅1.28077…−3=6.43844…u7=1.28077…
Δu7=∣1.28077…−1.28077…∣=7.99005E−8Δu7=7.99005E−8
u≈1.28077…
긴 나눗셈 적용:u−1.28077…4u3−4u2−3u+2=4u2+1.12310…u−1.56155…
4u2+1.12310…u−1.56155…≈0
다음을 위한 하나의 솔루션 찾기 4u2+1.12310…u−1.56155…=0 뉴턴-랩슨을 이용하여:u≈0.50000…
4u2+1.12310…u−1.56155…=0
뉴턴-랩슨 근사 정의
f(u)=4u2+1.12310…u−1.56155…
f′(u)찾다 :8u+1.12310…
dud(4u2+1.12310…u−1.56155…)
합계/차이 규칙 적용: (f±g)′=f′±g′=dud(4u2)+dud(1.12310…u)−dud(1.56155…)
dud(4u2)=8u
dud(4u2)
정수를 빼라: (a⋅f)′=a⋅f′=4dud(u2)
전원 규칙을 적용합니다: dxd(xa)=a⋅xa−1=4⋅2u2−1
단순화=8u
dud(1.12310…u)=1.12310…
dud(1.12310…u)
정수를 빼라: (a⋅f)′=a⋅f′=1.12310…dudu
공통 도함수 적용: dudu=1=1.12310…⋅1
단순화=1.12310…
dud(1.56155…)=0
dud(1.56155…)
상수의 도함수: dxd(a)=0=0
=8u+1.12310…−0
단순화=8u+1.12310…
렛 u0=1계산하다 un+1 까지 Δun+1<0.000001
u1=0.60961…:Δu1=0.39038…
f(u0)=4⋅12+1.12310…⋅1−1.56155…=3.56155…f′(u0)=8⋅1+1.12310…=9.12310…u1=0.60961…
Δu1=∣0.60961…−1∣=0.39038…Δu1=0.39038…
u2=0.50800…:Δu2=0.10160…
f(u1)=4⋅0.60961…2+1.12310…⋅0.60961…−1.56155…=0.60961…f′(u1)=8⋅0.60961…+1.12310…=6u2=0.50800…
Δu2=∣0.50800…−0.60961…∣=0.10160…Δu2=0.10160…
u3=0.50004…:Δu3=0.00796…
f(u2)=4⋅0.50800…2+1.12310…⋅0.50800…−1.56155…=0.04129…f′(u2)=8⋅0.50800…+1.12310…=5.18718…u3=0.50004…
Δu3=∣0.50004…−0.50800…∣=0.00796…Δu3=0.00796…
u4=0.50000…:Δu4=0.00004…
f(u3)=4⋅0.50004…2+1.12310…⋅0.50004…−1.56155…=0.00025…f′(u3)=8⋅0.50004…+1.12310…=5.12350…u4=0.50000…
Δu4=∣0.50000…−0.50004…∣=0.00004…Δu4=0.00004…
u5=0.5:Δu5=1.91092E−9
f(u4)=4⋅0.50000…2+1.12310…⋅0.50000…−1.56155…=9.78986E−9f′(u4)=8⋅0.50000…+1.12310…=5.12310…u5=0.5
Δu5=∣0.5−0.50000…∣=1.91092E−9Δu5=1.91092E−9
u≈0.50000…
긴 나눗셈 적용:u−0.54u2+1.12310…u−1.56155…=4u+3.12310…
4u+3.12310…≈0
u≈−0.78077…
해결책은u≈1.28077…,u≈0.50000…,u≈−0.78077…
뒤로 대체 u=cos(x)cos(x)≈1.28077…,cos(x)≈0.50000…,cos(x)≈−0.78077…
cos(x)≈1.28077…,cos(x)≈0.50000…,cos(x)≈−0.78077…
cos(x)=1.28077…:해결책 없음
cos(x)=1.28077…
−1≤cos(x)≤1해결책없음
cos(x)=0.50000…:x=arccos(0.50000…)+2πn,x=2π−arccos(0.50000…)+2πn
cos(x)=0.50000…
트리거 역속성 적용
cos(x)=0.50000…
일반 솔루션 cos(x)=0.50000…cos(x)=a⇒x=arccos(a)+2πn,x=2π−arccos(a)+2πnx=arccos(0.50000…)+2πn,x=2π−arccos(0.50000…)+2πn
x=arccos(0.50000…)+2πn,x=2π−arccos(0.50000…)+2πn
cos(x)=−0.78077…:x=arccos(−0.78077…)+2πn,x=−arccos(−0.78077…)+2πn
cos(x)=−0.78077…
트리거 역속성 적용
cos(x)=−0.78077…
일반 솔루션 cos(x)=−0.78077…cos(x)=−a⇒x=arccos(−a)+2πn,x=−arccos(−a)+2πnx=arccos(−0.78077…)+2πn,x=−arccos(−0.78077…)+2πn
x=arccos(−0.78077…)+2πn,x=−arccos(−0.78077…)+2πn
모든 솔루션 결합x=arccos(0.50000…)+2πn,x=2π−arccos(0.50000…)+2πn,x=arccos(−0.78077…)+2πn,x=−arccos(−0.78077…)+2πn
모든 솔루션 결합x=2π+2πn,x=23π+2πn,x=arccos(0.50000…)+2πn,x=2π−arccos(0.50000…)+2πn,x=arccos(−0.78077…)+2πn,x=−arccos(−0.78077…)+2πn
해를 10진수 형식으로 표시x=2π+2πn,x=23π+2πn,x=1.04719…+2πn,x=2π−1.04719…+2πn,x=2.46670…+2πn,x=−2.46670…+2πn