cos^2(x)+cos^2(3x)=1

해법

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

x = 0.78539 \dots + 2 πn, x = 2 π - 0.78539 \dots + 2 πn, x = 2.35619 \dots + 2 πn, x = - 2.35619 \dots + 2 πn, x = 0.39269 \dots + 2 πn, x = 2 π - 0.39269 \dots + 2 πn, x = 2.74889 \dots + 2 πn, x = - 2.74889 \dots + 2 πn, x = 1.17809 \dots + 2 πn, x = 2 π - 1.17809 \dots + 2 πn, x = 1.96349 \dots + 2 πn, x = - 1.96349 \dots + 2 πn

솔루션 단계

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

빼다

1

양쪽에서

cos^{2} (x) + cos^{2} (3 x) - 1 = 0

삼각성을 사용하여 다시 쓰기

- 1 + 10 cos^{2} (x) + 16 cos^{6} (x) - 24 cos^{4} (x) = 0

대체로 해결

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

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

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

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

cos (x) = - \frac{2 + 2}{2} : x = arccos (- \frac{2 + 2}{2}) + 2 πn, x = - arccos (- \frac{2 + 2}{2}) + 2 πn

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

cos (x) = - \frac{2 - 2}{2} : x = arccos (- \frac{2 - 2}{2}) + 2 πn, x = - arccos (- \frac{2 - 2}{2}) + 2 πn

모든 솔루션 결합

x = arccos (\frac{1}{2}) + 2 πn, x = 2 π - arccos (\frac{1}{2}) + 2 πn, x = arccos (- \frac{1}{2}) + 2 πn, x = - arccos (- \frac{1}{2}) + 2 πn, x = arccos (\frac{2 + 2}{2}) + 2 πn, x = 2 π - arccos (\frac{2 + 2}{2}) + 2 πn, x = arccos (- \frac{2 + 2}{2}) + 2 πn, x = - arccos (- \frac{2 + 2}{2}) + 2 πn, x = arccos (\frac{2 - 2}{2}) + 2 πn, x = 2 π - arccos (\frac{2 - 2}{2}) + 2 πn, x = arccos (- \frac{2 - 2}{2}) + 2 πn, x = - arccos (- \frac{2 - 2}{2}) + 2 πn

해를 10진수 형식으로 표시

x = 0.78539 \dots + 2 πn, x = 2 π - 0.78539 \dots + 2 πn, x = 2.35619 \dots + 2 πn, x = - 2.35619 \dots + 2 πn, x = 0.39269 \dots + 2 πn, x = 2 π - 0.39269 \dots + 2 πn, x = 2.74889 \dots + 2 πn, x = - 2.74889 \dots + 2 πn, x = 1.17809 \dots + 2 πn, x = 2 π - 1.17809 \dots + 2 πn, x = 1.96349 \dots + 2 πn, x = - 1.96349 \dots + 2 πn