Tính tổng sau: 15+17+19+21+...+73+75+77

Question

$15 + 17 + 19 + 21 + ... + 73 + 75 + 77$

$= (15 + 75) + (17 + 73) + ... + (43 + 47) + (45 + 77)$

= $\underset{15 s o á}{\underset{⏟}{90 + 90 + ... + 90 + 90}} + 122$

$= 90 . 15 + 122$ = 1472

Answer 1

Trả lời:

Giải bởi Vietjack

$15 + 17 + 19 + 21 + ... + 73 + 75 + 77$

$= (15 + 75) + (17 + 73) + ... + (43 + 47) + (45 + 77)$

= $\underset{15 s o á}{\underset{⏟}{90 + 90 + ... + 90 + 90}} + 122$

$= 90 . 15 + 122$ = 1472