$$$\ln^{3}\left(u\right)$$$의 도함수
사용자 입력
$$$\frac{d}{du} \left(\ln^{3}\left(u\right)\right)$$$을(를) 구하시오.
풀이
함수 $$$\ln^{3}\left(u\right)$$$는 두 함수 $$$f{\left(v \right)} = v^{3}$$$와 $$$g{\left(u \right)} = \ln\left(u\right)$$$의 합성함수 $$$f{\left(g{\left(u \right)} \right)}$$$이다.
연쇄법칙 $$$\frac{d}{du} \left(f{\left(g{\left(u \right)} \right)}\right) = \frac{d}{dv} \left(f{\left(v \right)}\right) \frac{d}{du} \left(g{\left(u \right)}\right)$$$을(를) 적용하십시오:
$${\color{red}\left(\frac{d}{du} \left(\ln^{3}\left(u\right)\right)\right)} = {\color{red}\left(\frac{d}{dv} \left(v^{3}\right) \frac{d}{du} \left(\ln\left(u\right)\right)\right)}$$거듭제곱법칙 $$$\frac{d}{dv} \left(v^{n}\right) = n v^{n - 1}$$$을 $$$n = 3$$$에 적용합니다:
$${\color{red}\left(\frac{d}{dv} \left(v^{3}\right)\right)} \frac{d}{du} \left(\ln\left(u\right)\right) = {\color{red}\left(3 v^{2}\right)} \frac{d}{du} \left(\ln\left(u\right)\right)$$역치환:
$$3 {\color{red}\left(v\right)}^{2} \frac{d}{du} \left(\ln\left(u\right)\right) = 3 {\color{red}\left(\ln\left(u\right)\right)}^{2} \frac{d}{du} \left(\ln\left(u\right)\right)$$자연로그 함수의 도함수는 $$$\frac{d}{du} \left(\ln\left(u\right)\right) = \frac{1}{u}$$$:
$$3 \ln^{2}\left(u\right) {\color{red}\left(\frac{d}{du} \left(\ln\left(u\right)\right)\right)} = 3 \ln^{2}\left(u\right) {\color{red}\left(\frac{1}{u}\right)}$$따라서, $$$\frac{d}{du} \left(\ln^{3}\left(u\right)\right) = \frac{3 \ln^{2}\left(u\right)}{u}$$$.
정답
$$$\frac{d}{du} \left(\ln^{3}\left(u\right)\right) = \frac{3 \ln^{2}\left(u\right)}{u}$$$A