a_{n}, a_{n} - d, a_{n} - 2 d, a_{n} - 3 d, \dots

${a_n, a_n - d, a_n - 2d, a_n - 3d, \ldots}$

a_{n}, a_{n} - d, a_{n} - 2 d, a_{n} - 3 d, \dots

$a_n, a_n - d, a_n - 2d, a_n - 3d, \ldots$

a_{n}

$a_n$

a_{n}

$a_n$

1

d

$d$

1

\dots

$\ldots$

1

Lisa

OK

Error