Very good traditional mathematician way of explaining calculus(differential/integral) .When I first encounter 350years old calculus in upper secondary school (S-4 and S-5 later). There are a few PHD degree experts in internet, try to change the basic way of explaining fundamental calculus (non mathematicianWay! ). Even the expert/experianced calculus people will be trapped and deviate from normal ! I see the viewers comments/feedbacks .Majority of them Very Confused ask them why , they themselve do not know how to explain why ! And they just follow the mathsWay to get the funny answer and try to prove Maths are 100% all wrong ! Their way of mathsWay containing many loopholes and violet mathematician basic definitions ! This is similar to somePHD-Expert to prove that our Earth is 'FLAT-PANcake' and try to Abandon the 'Round-Earth' . Thus your way of teaching calculus in internet is Excellent ! Good keep it up !