Đáp án:
Giải thích các bước giải:
$A$ = $1,1$ $-$ $2,2$ $+$ $3,3$ $-$ $4,4$ $+$ $5,5$ $-$ $6,6$ $+$ $7,7$ $-$ $8,8$ $+$ $9,9$ $-$ $11$ $+$ $12,1$
$A$ = ( $1,1$ $+$ $3,3$ $+$ $5,5$ $+$ $7,7$ $+$ $9,9$ $+$ $12,1$ ) $-$ $2,2$$-$ $4,4$ $-$ $6,6$ $-$ $8,8$ $-$ $11$
$A$ = $39,6$ $-$ $2,2$$-$ $4,4$ $-$ $6,6$ $-$ $8,8$ $-$ $11$
$A$ = $6,6$