[tex]\it -5,\ a_2,\ a_3,\ a_4,\ a_5,\ a_6,\ 13\ sunt\ termeni\ ai\ unei\ progresii\ aritmetice \Rightarrow \\ \\ \Rightarrow a_1=-5,\ \ a_7=13 \Rightarrow r=\dfrac{13+5}{6}=\dfrac{18}{6}=3\\ \\ \\ Progresia\ va\ fi: -5,\ -2,\ 1,\ 4,\ 7,\ 10,\ 13, ...[/tex]
