Răspuns:
[tex]\boldsymbol{ \red{ 11}}[/tex]
Explicație pas cu pas:
[tex]a_5=a_2+(5-2)r=a_2+3r[/tex]
[tex]\implies a_2=a_5-3r[/tex]
[tex]a_{10}=a_7+(10-7)r[/tex]
[tex]\implies a_{10}=a_7+3r[/tex]
[tex]\Rightarrow a_2+a_{10}=a_5-3r+a_7+3r=a_5+a_7=\bf11[/tex]
[tex]\boxed{\boldsymbol{a_{k+1} = a_{k} + r}}[/tex]
