Question

Cine ma ajuta si pe mine va rogg? :(
1)a) a55 stiind ca a1=3 si r=2
b)a120 stiind ca a2=7 si r=4
2)a) a1+a5=14 a7-a3=8
b)a2+a8=2 a3+a4=-1

Answer 1

1.
a) a55=a1+45r=3+45•2=3+90=93
b) a120=a2-r+119r=a2+118r=7+118•2=7+236=243

2.
a) a1+a5=14 <=>a1+a1+4r=14 <=>a1+2r=7
a7-a3=8 <=>a1+6r-a1-2r=8 <=>4r=8=>r=2
a1=7-4=3
b)a2+a8=2 <=>a1+r+a1+7r=2<=>2a1+7r=2
a3+a4=-1<=>a1+2r+a1+3r=-1<= 2a1+5r=-1
2a1=2-7r
2-7r+5r=-1<=>-2r=-3=>r=2/3
a1=(2-14/3)/2=-8/3/2=-4/3