Respuesta :

[tex]a_2=a_1+d[/tex]
[tex]a_3=a_2+d=a_1+2d[/tex]
[tex]a_4=a_3+d=a_1+3d[/tex]
...
[tex]a_{15}=a_1+14d[/tex]

Since [tex]a_1=-3[/tex] and [tex]a_{15}=53[/tex], the common difference [tex]d[/tex] is

[tex]53=-3+14d\implies d=4[/tex]