E\times 03-5 (15)
1+2+3+4+5+6
+7+8+9+10=
(16)
1+2+3+4+cdots+20=
(17)
1+2+cdotscdots+100=
(18)
1ubrace(1+ubrace(3+5ubrace)_(2)+ubrace(+7+9ubrace)_(2)ubrace)_(2)
use matlab