The differentiability and continuity of function f (x) = | cosx | are discussed

The differentiability and continuity of function f (x) = | cosx | are discussed

On the whole number axis, it is continuous;
K is an integer, except π / 2 + 2K π and π / 2-2k π

It is verified that when (x, y) tends to (0,0), the limit of u = x + Y / X-Y does not exist. How does (x, y) tend to (0,0) make (1) Limu = 1, (2) Limu = 2?

Let (x, y) tend to (0,0) along the path of y = KX, then the original formula is Lim [(x + KX) / (x-kx))] = Lim [(1 + k) / (1-k)]. It can be seen that when k takes different values, its limit is different, which contradicts the uniqueness of the limit, so the limit does not exist. (1) to make Limu = 1, that is, to make k = 0, that is, (x, y) along y =

Why does the limit of limx →∞|x | (x + 1) / x ^ 2 not exist

Limx → + ∞ | x | (x + 1) / x ^ 2 = 1 and limx → - ∞ | (x + 1) / x ^ 2 = - 1