Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
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74 Calculul cu diferent¸e<br />
Problema 5.0.21 Dacăf,g : X → R, atunci<br />
=<br />
[x0,...,xm;fg] =<br />
m<br />
[x0,...,xk][xk,...,xm;g]<br />
k=0<br />
Demonstrat¸ie. Prin induct¸ie dupăm<br />
m = 1<br />
[x0,x1;fg] = f(x0)[x0,x1;g]+[x0,x1;f]g(x1) =<br />
= f(x0) g(x1)−g(x0)<br />
x1 −x0<br />
+ f(x1)−f(x0)<br />
g(x1) =<br />
x1 −x0<br />
= f(x1)g(x1)−f(x0)g(x0)<br />
x1 −x0<br />
Presupunem relat¸ia a<strong>de</strong>vărată pentru m−1, adică<br />
m−1 <br />
[x0,...,xm−1;fg] = [x0,...,xk;f][xk,...,xm−1;g]<br />
[x0,...,xn;fg] <strong>de</strong>f<br />
=<br />
1<br />
xm −x0<br />
1<br />
xm −x0<br />
k=0<br />
([x1,...,xm;fg]−[x0,...,xm−1;fg]) =<br />
m−1 <br />
([x1,...,xk+1;f][xk+1,...,xn;g]−[x0,...,xk;f][xk,...,xn−1;g])<br />
k=0<br />
Adunând s¸i scăzând sub simbolul <strong>de</strong> însumare[x0,...,xk;f][xk+1,...,xm;g]<br />
s¸i grupând convenabil se obt¸ine<br />
[x0,...,xm;fg] =<br />
k=0<br />
1<br />
xm −x0<br />
m−1<br />
<br />
[x0,...,xk;f]([xk+1,...,xm;g]−[xk,...,xm−1;g])+<br />
k=0<br />
<br />
m−1 <br />
+ [xk+1,...,xn;g]([x1,...,xk+1;f]−[x0,...,xkf]) =<br />
=<br />
1<br />
xn −x0<br />
+<br />
=<br />
m−1<br />
<br />
(xm −xk)[x0,...,xk;f][xk,...,xm;g]+<br />
k=0<br />
m<br />
<br />
(xk −x0)[x0,...,xn;f][xk,...,xn;g] =<br />
k=1<br />
1<br />
xn −x0<br />
<br />
(xm −x0)[x0;f][x0,...,xn;g]+