As someone who's taking a university entrance course in Calculus I find these kind of "calculus made easy" pamphlets irritatingly trite.
The hard part isn't the highest level concepts, which are actually fairly easy to grasp and somewhat intuitive.
The hard part is all the foundational knowledge required to solve actual math problems with Calculus.
The most difficult parts of Calculus (for me at least) are:
1. Having a very thorough grasp of the groundwork / assumed knowledge. Good enough that you can correctly solve an unexpected problem, from completing the square to long division of polynomials to an equation involving differentials.
2. Understanding and correctly applying the notation and graphing techniques, from Leibniz notation to sketching curves.
This is why large books and courses exist covering only introductory Calculus, not even beginning to scrape the surface of more advanced math.
The hard part isn't the highest level concepts, which are actually fairly easy to grasp and somewhat intuitive.
The hard part is all the foundational knowledge required to solve actual math problems with Calculus.
The most difficult parts of Calculus (for me at least) are:
1. Having a very thorough grasp of the groundwork / assumed knowledge. Good enough that you can correctly solve an unexpected problem, from completing the square to long division of polynomials to an equation involving differentials.
2. Understanding and correctly applying the notation and graphing techniques, from Leibniz notation to sketching curves.
This is why large books and courses exist covering only introductory Calculus, not even beginning to scrape the surface of more advanced math.