I want to aproach the undertanding of the trigonometric function based on the concept of relacional undertanding, but I have problems to came up with and problemic situation for it. I mean I don´t want the first aproach to the students to be the typical unit circumference thing, I want they to comprenhend the how and why the trigonimetric function pop up the way they do.
For example: I read about some formulas for some geometric objects, there is the formulas and no more; by the other hand, in other place the authors intuitively explaned the notion of area in a rectangle, ans they use it for came up with all the formulas that in the first paper only apear of nowhere (parallelogram, traprice, irregular trapezoid, triangle and even circle).
If someone could recomend me some book to search about this, or give me some orientention. Thank for your time.