Progresii Geomterice
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Transcript of Progresii Geomterice
Progresii GeomtericeGhita Razvan IX -G
Un sir de numere in care fiecare termen se obtine din precedentul prin inmultire cu acelasi numar ( ratie ) se numeste Progresie Geometrica.
Progresii Geomterice Notatii:
p.g. (bn)
b1 ; b2 ; b3 .......bn
q = ratie
Formule :
bn = bn−1 • q
bn = b1 • qn−1
Sn = b1 • qn - 1 /q-1
b2 = √b1• b3
Aplicatii:
Ex 1:
p.g.
bn = bn−1 • q
b1 = 3 ; q = 2
primii 5 termeni = ?
b2 = b1 • q => b2 =3 • 2 = 6
b3 = b2 • q => b3 = 6 • 2 = 12
b4 = b3 • q => b4 = 12 • 2 = 24
b5 = b4 • q => b5 = 24 • 2 = 48
p.g. = 3 ; 6 ; 12 ; 24 ; 48
Ex 2:
b1 = 2
b2 = 6
b5 = ?
b2 = b1 • q
6 =2 • q => q = 3
b5 = b1 • q5−1
b5 = 2 • 34 = 2 • 81 = 162
Ex 2:
a14 = ?
a4 = 7 | a4 = a1 + (4-1)r
a9 = 22 | a9 = a1+ (9-1)r
7 = a1 + 3r a1+ 3r = 7(-1) -a1 -3r = -7
22 = a1+ 8r a1+ 8r = 22 a1+ 8r = 22
/ 5r = 15 => r= 3
a14 = a1 + (14-1)r
a14 = -2 + 13 • = 37 a1 + 9 = 7 => a1 = -2