Question

Afla nr de termeni:a)1,2,3,...60.b)2,4,6,....120.c)2,4,6,...400.d)94,96,98,...3
00.e)1,3,5,7,...97.f)3,6,9,12,...102.

Answer 1

a)   1, 2, 3, .......... 60 → 60 numere in sir ( ratia = 1 )

b)   2, 4,  6,  .........120 → 60 numere in sir ( sir crescator din 2 in 2 al primelor 60 de numere consecutive pare nenule )

( 120 - 2 ) : 2 + 1 = 118 : 2 = 59 + 1 = 60 sau 120 : 2 = 60 numere

c)   2, 4, 6,  .......400 → 200 numere in sir (  primele 200 numere pare consecutive, nenule )  ratia = 2 ( 4- 2 = 2;   6 - 4 = 2 .....)

( 400 - 2 ) : 2 + 1 = 398 : 2 + 1 = 199 + 1 = 200

d) 94, 96, 98, ...300  → 104 numere in sirul crescator din 2 in 2 al numerelor pare consecutive da la 94 pana la 300  ( ratia = 2 )

( 300 - 94 ) : 2 + 1 = 206 : 2 + 1 = 103 + 1 = 104  

e) 1, 3, 5, 7, ... 97 → 49 numere in sir ( termeni ai progresiei aritmetice cu ratia=2)

( 97 - 1 ) : 2 + 1 = 96 : 2 + 1 = 48 + 1 = 49  sau ( 97 + 1 ) : 2 = 98 : 2 = 49 numere in sir

f)   3, 6, 9, 12, ... 102 → 34 termeni ai sirului ( cu ratia 3 )

( 102 - 3 ) : 3 + 1 = 99 : 3 + 1 = 33 + 1 = 34