There are several points in Unit 1 of the Integral Calculus course where the learner is expected to know and use concepts that have not been taught yet. In some cases, these concepts are covered in later lessons. In others, they can only be found in other courses that are not in the mainline Math curriculum.

1. Exercise/quiz problems with solutions not yet covered.
Example: Prior to the unit on "integration by parts," there is an exercise and/or quiz (I do not recall which one(s) [I reported them at the time I encountered them]) that gives problems requiring integration by parts to solve.

2. Lessons expecting knowledge of concepts not covered.
Example: The "Integration with partial fractions" video in lesson 18 expects learners to already know partial fraction decomposition. Lessons on partial fraction decomposition are not covered in any of the mainline math courses (Algebra 1/2, Trig, College Algebra, PreCalc, etc...) in Khan's curriculum. The videos can only be found in the "Algebra (all content)" course and the "Get ready for AP Calculus" course.

These are not the only instances of this problem occurring within the unit.

I believe it would benefit future learners for this unit (and possibly others if the problem is more wide spread throughout the course) to be reviewed and restructured to ensure topics appear in sequence and in totality.