Question

progresia aritmetica (an)n>1 de ratie r este definita prin anumite elemente date .

determinati , in fiecare din cazuri , elementul cerut.
1)a1=-3,r=-2calculati a20
2)a30=60,r=2calculati a1
3)a1=3,a27=81 calculati r
4)a3=8,a4=5 calculati a1,r
5)a2+a40=16,a1 a5=28c calculati a1,r
6)a2-a6+a4=-7,a8-a7=2a4 calculati a1,r
7)a1a2a3=120,a1+a2+a3=15 calculati a1 si r
8)a2+a2+a2+a2+a2=45,r=2 calculati a1
1 2 3 4 5
9)a2 +a4+...+a2n=126,a2+a2n=42 calculatin
10) r=4,a1a2a3a4=585 calculatia1
UGENT

Answer 1

a)a20=a1+(n-1)r=a1+19r=-3-48=-51
=>a20=-51
b)a30=a1+29r=60
=>a1=60-58=2
=>a1=2
c)a27=a1+26r=81
=>r=78/26
=>r=3
d){a1+2r=8 (1)
    a1+3r=5  (2)
=>(1)-(2)=>-r=3=>r=-3
=>a1=14
=>r=-3;a1=14