In case you're not already aware, the expression
is called the "difference quotient" and represents the average rate of change of a function
over an interval
.
For the function
, by substituting
we get

Then the difference quotient is


where the last equality holds as long as
.
Answer:
Haha proofs are an interesting thing. Usually, nothing is to scale, which is why you can't measure anything. They are pretty annoying, but it helps to know why certain things are the way that they are and develop justification skills for higher level math.
Sorry to discourage you, but you're going to see "Justify" quite a lot in calculus and beyond which is basically a more informal version of a proof
you can never escape it tbh lol