Question

intr-o progresie aritmetica (an) se cunosc a1 si r.Sa se gaseasca (an) daca: a)a1=-2,r=0,5,n=12 b)a1=3,r=-1,5,n=19 c)a1=-2,5,r=-2,n=50 d)a1=3 supra 7,r=1 supra 3,n=25.

Answer 1

an = a1+(n-1)xr

a) a12 = 2+(12-1)x0,5 = 2+11x0,5 = 2+5,5 = 7,5 ;

b) a19 = 3+(19-1)x(-1,5) = 3+18x(-1,5) = 3-27 = -24 ;

c) a50 = 2,5+(50-1)x(-2) = 2,5+49x(-2) = 2,5-98 = 95,5 ;

d) a25 = 3+(25-1)x(3/7) = 3+24x(3/7) = 3+72/7 = (21+72)/7 = 93/7 ;