... →∞.∞k=0xkf(x)= 1 1 − x[ 1, 1) 0 ≤ r< ;1 [−r, r]Sk(x) =1+ x + ···+ xk= 1 − xk +1 1 − x[−r, r]sup|x|≤r|Sk(x) − f(x)| =sup|x|≤rxk +1 1 − x=rk +1 1 − r→ 0, k →∞.f ( 1, 1) 2n,np, ... y)=(x + y)sin 1 xsin 1 y. a 12 ,a 21 a =0f(x, y)=x2− y2x2+ y. a 12 =0,a 21 =1 af(x, y)=xyx2+ y2. a 12 = a 21 =0 af(x, y)=x sin 1 y. a 12 =0 a 21 a =0a = a 12 = a 21 f : X ×Y ... y).f(x)= 1 x,x∈ (0, +∞)EEE RN : E → R (N1)(N2)(N3)Rnx → max 1 i≤n|xi| x →ni =1 |xi|xN 1 ,N2M,mmN 1 (x) ≤ N2(x) ≤ MN 1 (x), ∀x ∈ E.E f 1 , ··· ,fnET : E → Rn,x 1 f 1 +...