Learn Calculus With These Four Online Courses

https://lifehacker.com/learn-calculus-with-these-four-online-courses-1836377912/amp

Four Online Free Calculus Courses:
1. http://www-math.mit.edu/~djk/calculus_beginners/

2. “Calculus Made Easy” (1910 )

http://calculusmadeeasy.org/

3. “Essence of Calculus” (12 short videos, with Chinese subtitle)

4. [Best👍] “Calculus” (MIT Prof Gilbert Strang)

https://ocw.mit.edu/resources/res-18-001-calculus-online-textbook-spring-2005/textbook/

Walter Bradley Center Fellow Discovers Longstanding Flaw in Elementary Calculus

https://mindmatters.ai/2019/04/walter-bradley-center-fellow-discovers-longstanding-flaw-in-elementary-calculus/

… The paper on the proof of the second derivative (Quotient rule) :

https://www.dropbox.com/s/mv6npb3tpe76xjl/4.pdf?dl=0

Reference:

Faà di Bruno Fomula

\boxed{ (f\circ H)^{(n)} =\displaystyle\sum_{\sum_{j=1}^n j\,m_j=n} \frac{n!}{m_!\ldots m_n!}\, \bigl(f^{(m_1+\ldots+m_n)})\circ H\bigr)\, \prod_{j=1}^n \left(\frac{H^{(j)}}{j!}\right)^{m_j} }