Question

sa se afle progresia geometrica daca a1=33 si S26=1053

Answer 1

[tex]S_{26}=1053\\ \frac{a_1+a_{26}}{2}\cdot26=1053\\ \\(a_1+a_{26})\cdot13=1053\\ a_1+a_1+25r=1053:13\\ 2\cdot33+25r=81\\ 25r=81-66=15\\ r=\frac{15}{25}=\frac{3}{5}[/tex]