Question

fie o progresie aritmerica cu a1=7 si r=-2 determinati s12

dau coroana!!​

Answer 1

Răspuns:

Explicație pas cu pas:

Answer 2

$\it a_1=7,\ r=-2 \Rightarrow a_{12}=a_1+11r=7=22=-15\\ \\ S_{12}=\dfrac{(a_1+a_{12})\cdot12}{2}=(7-15)\cdot6=-8\cdot6=-48$