a) 2;4;6........54= 2* x (1,2,3,....27); sirul are 27 termeni
b) 4;7;10........76; primul termen =1+3*1=4
ultimul termen = 76; 76-1=75; 75:3=25
sirul are 25 de termeni.
c) 2;7;12.......77; avem o diferenta de5 intre fiecare termen,r=5
a1=5*1-3; a2= 5*2-3; a3=5*3-3.....
an=77=5*x-3; (77+3):5= 16
Sirul are 16 termeni.