A local linear approximation can be found by taking the first two terms of the Taylor series of the function.
For f(x) = e^2x at x = 0,
f(x) ≈ f(0) + f'(0)(x)
= 1 + 2x
The term "motif" refers to recurring ideas or thoughts that act as a unifying idea, and it sometimes develops as a commentary on characterization or on the central ideas in the work. Sometimes motifs recur so frequently that they enhance the meaning of the novel and often rise to symbolic importance.
There teaching, the way they teach there students, in other countries they have more advanced teaching. P.S this is just my reasoning there are plenty other answers to this question.