Răspuns:
Explicație pas cu pas:
11. a1=5/2, r=5/6, atunci
[tex]a_{4}=a_{1}+3*r=\frac{5}{2}+3*\frac{5}{6}=\frac{5}{2}+\frac{3*5}{6}=\frac{5}{2}+\frac{5}{2}=\frac{10}{2}=5\\ Ex12\\a_{2}=10, a_{7}=18\frac{1}{2}. r=?\\ a_{7}=a_{2}+5*r,\\18\frac{1}{2}=10+5*r\\5*r=18,5-10\\5*r=8,5\\r=8,5:5=1,7[/tex]
