Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
Culegere de probleme de Analiz˘a numeric˘a
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
68 Calculul cu diferent¸e<br />
Problema 5.0.7 Aplicat¸ie. Vom stabili o formulă explicită pentru calculul sumei<br />
Sm,r = 1 r +2 r +3 r +···+m r<br />
cu ajutorul diferent¸elor lui 0.<br />
r<br />
<br />
m+1<br />
Sm,r = ∆<br />
i+1<br />
i=1<br />
i 0 r<br />
p<br />
<br />
p<br />
f(ap) = ∆<br />
k<br />
j=0<br />
k hf(a) ∆m m<br />
h f(a) = (−1)<br />
i=0<br />
m−i<br />
<br />
m<br />
f(a+ih)<br />
i<br />
f(x) = xr pr p<br />
<br />
p<br />
= f(p) = ∆<br />
k<br />
k=0<br />
k 0 r , p = 1,2,...,m<br />
1r <br />
1<br />
= ∆<br />
0<br />
0 0 r <br />
1<br />
+ ∆<br />
1<br />
1 0 r<br />
2r <br />
2<br />
= ∆<br />
0<br />
0 0 r <br />
2<br />
+ ∆<br />
1<br />
1 0 r <br />
2<br />
+ ∆<br />
2<br />
2 0 r<br />
...<br />
mr <br />
m<br />
= ∆<br />
0<br />
0 0 r <br />
m<br />
+ ∆<br />
1<br />
1 0 r <br />
m<br />
+···+ ∆<br />
m<br />
m 0 r<br />
m<br />
<br />
j j +1 m<br />
Sm,r = + +···+ ∆<br />
j j j<br />
j 0 r =<br />
j=1<br />
j=1<br />
Deoarece dacă m > r, ∆o0r = 0 pentru j = r +1,m iar pentru m < r,<br />
r<br />
<br />
m+1<br />
∆<br />
j +1<br />
j 0 r<br />
<br />
m+1<br />
= 0, pentru j = m+1,m+2,...,r.<br />
j +1<br />
Cazuri particulare <br />
m+1 m+1<br />
Sm,1 = ∆0 = =<br />
2 2<br />
m(m+1)<br />
, ∆0 = 1<br />
<br />
2<br />
2 m+1 ∆0<br />
Sm,2 =<br />
2 1 +<br />
2 2 m+1 ∆ 0 m(m+1)(2m+1)<br />
=<br />
3 2 6<br />
3 m+1 ∆0<br />
Sm,3 =<br />
2 1 +<br />
2 3 m+1 ∆ 0<br />
3 6 +<br />
3 3 m+1 ∆ 0<br />
4 6 =<br />
<br />
m(m+1)<br />
2<br />
Problema 5.0.8 Să se <strong>de</strong>monstreze formula<br />
(prin induct¸ie).<br />
∆ m h<br />
1<br />
x =<br />
(−1) m m!h m<br />
x(x+h)...(x+mh)<br />
2