Question

Efectuați :
a) 7+9+11+...+2013-5-7-9-...-2011=
b) 11+12+13+...+78=
c)5+10+15+...+95=
d)5+8+11+...+305=
VĂ ROG AJUTAȚI-MĂ !!!

Answer 1

a) 7+9+11+...+2013-5-7-9-...-2011=
observam ca 7-7=0 ; 9-9=0....2011-2011=0
=-5+2013=2008
b) 11+12+13+...+78=
nr de numere in sir 78-11+1=68
le grupam
(11+78)*68/2=89*34=3026

c)5+10+15+...+95=5(1+2+3+...+19)=5*19*20/2=50*19=950
d)5+8+11+...+305=
pasul 8-5=3
nr de numere in sir (305-5):3+1=101
nr din mijloc 5+50*3=5+150=155
le grupam
(5+305)*100/2+155=310*50+155=15500+155=15655