1) <em>x1=14, d=0,5; xn1=17,5; xn2=19; xn3=34; n1, n2, n3 = ?</em>
xn1=x1+d*(n1-1) => 0,5(n1-1)=17,5-14=3,5 => n1-1=3,5/0,5=7 => <u>n1=8</u>
xn2=x1+d*(n2-1) => 0,5(n2-1)=19-14=5 => n2-1=5/0,5=10 => <u>n2=11</u>
xn3=x1+d*(n3-1) => 0,5(n3-1)=34-14=10 =>n3-1=10/0,5=20 => <u>n3=21</u>
2) <em>(an); a1=-1,2; d=3; a4, a8, a21 = ?</em>
a4=a1+3d=-1,2+9=<u>7,8</u>
a8=a1+7d=-1,2+21=<u>19,8</u>
a21=a1+20d=-1,2+60=<u>58,8</u>