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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72 Calculul cu diferent¸e<br />
Solut¸ie. Dacă F este o solut¸ie a ecuat¸iei cu diferent¸e<br />
are loc formula <strong>de</strong> sumare<br />
∆hF(x) = f(x)<br />
m<br />
f(a+jh) = F[a+(m+1)h]−F(a)<br />
j=0<br />
∆hF(x) = F(x+h)−F(x) = x, x = a,a+h,...,a+mh<br />
a+mh <br />
x=a(h)<br />
∆hF(x) = f(x), F(x) = u(x)v(x)<br />
∆hu(x)v(x) = u(x)∆hv(x)+∆hu(x)v(x+h)<br />
u(x)∆hv(x)+<br />
a+mh <br />
x=a(h)<br />
<br />
<br />
v(x+h)∆hu(x) = u(x)v(x)<br />
u(x) = x, ∆v(x) = b x ⇒ v(x) = bx<br />
m<br />
x=0<br />
<br />
<br />
b−1<br />
xb x = x bx<br />
m+1<br />
0<br />
−<br />
m<br />
x=0<br />
b−1<br />
b x<br />
b−1 =<br />
a+(m+1)h<br />
a<br />
= (m+1) bm+1 1<br />
−<br />
b−1 b−1 (b+b2 +···+b m+1 ) = (m+1) bm+1<br />
b−1 − bm+2 −b<br />
(b−1) 2<br />
<br />
−cos x−<br />
u(x) = x, ∆v(x) = sinx ⇒ v(x) =<br />
h<br />
<br />
2<br />
2sin h<br />
2<br />
<br />
a+mh cos x−<br />
xsinx = −x<br />
x=a<br />
h<br />
<br />
2<br />
2sin h<br />
<br />
a+(m+1)h<br />
a+mh<br />
cos x+<br />
+<br />
<br />
a x=a<br />
2<br />
h<br />
<br />
2<br />
2sin h<br />
2<br />
<br />
Deoarece ∆hF(x) = cos x+ h<br />
<br />
este satisfăcută pentru F(x) =<br />
2<br />
sinx<br />
2sin h<br />
2<br />
rezultă că avem<br />
a+mh <br />
<br />
cos x+<br />
x=a<br />
h<br />
<br />
=<br />
2<br />
sinx<br />
2sin h<br />
<br />
a+(m+1)h<br />
<br />
<br />
<br />
a<br />
2