Question

1.Se considera progresia aritmetica cu a1=3 si r =5. Calculați a2,a3,a4,a10,a25,S25

Answer 1

Răspuns:

a2=a1+(2-1)•r=3+1•5=8

a3=a1+(3-1)•r=3+2•5=13

a4=a1+(4-1)•r=3+3•5=18

a10=a1+(10-1)•r=3+9•5=48

a25=a1+(25-1)•r=3+24•5=123

$s25 = \frac{(a1 + a25) \times 25}{2} = \frac{3 + 123}{2} = 62.5$